partitioning - How to extend the Size of my Ubuntu Partition

I have Installed Ubuntu 13.04 on my pre-installed Windows8 sony laptop with HDD of 500Gb.

There are a few partitions present by default like recovery ,etc.

I have created a few other partitions of 200 GB and 100 GB on /dev/sda7 and /dev/sda8 respectively. My Windows 8 is installed on /dev/sda5 while I have installed Ubuntu on /dev/sda11 with swap on /dev/sda12.

Now, I want to shrink my Windows 8 drive which is 109 GB and extend the Ubuntu partition of 15 GB by using the unallocated space from the earlier drive.

I tried using GParted via LiveUSB and performing the SWAP-OFF but I was unsuccessful.

Please suggest me a way ASAP.

Thanks.