partitioning - The volume boot has only 40mb disk space remaining

When I install the software updates with "Update Manager", there is a pop up alert which tells me "The volume "boot" has only 0 byte disk space remaining

run sudo fdisk -l in a terminal, and output:

Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0c7a859b
   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      206847      102400    7  HPFS/NTFS/exFAT
/dev/sda2          206848   280451071   140122112    7  HPFS/NTFS/exFAT
/dev/sda3       280451072   618371071   168960000    7  HPFS/NTFS/exFAT
/dev/sda4       618373118   976768064   179197473+   f  W95 Ext'd (LBA)
/dev/sda5       763730163   976768064   106518951    7  HPFS/NTFS/exFAT
/dev/sda6       618373120   626370559     3998720   83  Linux
/dev/sda7       626372608   630370303     1998848   82  Linux swap / Solaris
63.59 GB space **free** after /dev/sda7

lsblk output:

NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda      8:0    0 465.8G  0 disk
├─sda1   8:1    0   100M  0 part
├─sda2   8:2    0 133.6G  0 part
├─sda3   8:3    0 161.1G  0 part
├─sda4   8:4    0     1K  0 part
├─sda5   8:5    0 101.6G  0 part
├─sda6   8:6    0   3.8G  0 part /
└─sda7   8:7    0   1.9G  0 part [SWAP]
sr0     11:0    1  1024M  0 rom