16.04 - Error purging older kernel

Whatever I try to do whether installing new software, or if I try sudo apt-get upgrade

I always get error
Sometimes this:(when I tried sudo apt-get upgrade)

Reading package lists... Done
Building dependency tree
Reading state information... Done
You might want to run 'apt-get -f install' to correct these.
The following packages have unmet dependencies:
 linux-image-generic-hwe-16.04 : Depends: linux-image-4.15.0-47-generic but it is not installed
 linux-modules-extra-4.15.0-43-generic : Depends: linux-image-4.15.0-43-generic but it is not installed or
                                                  linux-image-unsigned-4.15.0-43-generic but it is not installed
 linux-modules-extra-4.15.0-45-generic : Depends: linux-image-4.15.0-45-generic but it is not installed or
                                                  linux-image-unsigned-4.15.0-45-generic but it is not installed
 linux-modules-extra-4.15.0-47-generic : Depends: linux-image-4.15.0-47-generic but it is not installed or
                                                  linux-image-unsigned-4.15.0-47-generic but it is not installed
E: Unmet dependencies. Try using -f.

Sometimes this:(when I tried sudo apt-get purge linux-image-4.15.0-30-generic)

Building dependency tree
Reading state information... Done
You might want to run 'apt-get -f install' to correct these:
The following packages have unmet dependencies:
 linux-image-generic-hwe-16.04 : Depends: linux-image-4.15.0-47-generic but it is not going to be installed
 linux-modules-extra-4.15.0-30-generic : Depends: linux-image-4.15.0-30-generic but it is not going to be installed or
                                                  linux-image-unsigned-4.15.0-30-generic but it is not going to be installed
 linux-modules-extra-4.15.0-43-generic : Depends: linux-image-4.15.0-43-generic but it is not going to be installed or
                                                  linux-image-unsigned-4.15.0-43-generic but it is not going to be installed
 linux-modules-extra-4.15.0-45-generic : Depends: linux-image-4.15.0-45-generic but it is not going to be installed or
                                                  linux-image-unsigned-4.15.0-45-generic but it is not going to be installed
 linux-modules-extra-4.15.0-47-generic : Depends: linux-image-4.15.0-47-generic but it is not going to be installed or
                                                  linux-image-unsigned-4.15.0-47-generic but it is not going to be installed
E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).

What should I do, it has become very hard to even install new software. I was trying to install R but again failed due to these (probably kernel unmet dependencies)

Output of sudo apt-get -f install:

Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  amd64-microcode intel-microcode iucode-tool libpython-all-dev libsodium18 libvpx3:i386 linux-headers-4.15.0-32 linux-headers-4.15.0-32-generic
  linux-headers-4.15.0-33 linux-headers-4.15.0-33-generic linux-headers-4.15.0-34 linux-headers-4.15.0-34-generic linux-headers-4.15.0-43
  linux-headers-4.15.0-43-generic linux-headers-4.15.0-45 linux-headers-4.15.0-45-generic linux-headers-4.15.0-47
  linux-headers-4.15.0-47-generic linux-headers-generic-hwe-16.04 linux-image-4.15.0-30-generic linux-image-4.15.0-32-generic
  linux-image-4.15.0-33-generic linux-image-4.15.0-34-generic linux-modules-4.15.0-30-generic linux-modules-4.15.0-32-generic
  linux-modules-4.15.0-33-generic linux-modules-4.15.0-34-generic linux-modules-extra-4.15.0-30-generic linux-modules-extra-4.15.0-32-generic
  linux-modules-extra-4.15.0-33-generic linux-modules-extra-4.15.0-34-generic python-all python-all-dev python-pip python-pip-whl python-wheel
  qtdeclarative5-controls-plugin qtdeclarative5-dialogs-plugin thermald
Use 'sudo apt autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 330 not upgraded.
2 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Setting up initramfs-tools (0.122ubuntu8.11) ...
update-initramfs: deferring update (trigger activated)
Setting up linux-firmware (1.157.21) ...
update-initramfs: Generating /boot/initrd.img-4.15.0-39-generic
W: Possible missing firmware /lib/firmware/i915/kbl_guc_ver9_14.bin for module i915
W: Possible missing firmware /lib/firmware/i915/bxt_guc_ver8_7.bin for module i915
cat: write error: No space left on device
update-initramfs: failed for /boot/initrd.img-4.15.0-39-generic with 1.
dpkg: error processing package linux-firmware (--configure):
 subprocess installed post-installation script returned error exit status 1
Processing triggers for initramfs-tools (0.122ubuntu8.11) ...
update-initramfs: Generating /boot/initrd.img-4.15.0-39-generic
W: Possible missing firmware /lib/firmware/i915/kbl_guc_ver9_14.bin for module i915
W: Possible missing firmware /lib/firmware/i915/bxt_guc_ver8_7.bin for module i915
cat: write error: No space left on device
update-initramfs: failed for /boot/initrd.img-4.15.0-39-generic with 1.
dpkg: error processing package initramfs-tools (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 linux-firmware
 initramfs-tools
E: Sub-process /usr/bin/dpkg returned an error code (1)