I bought yesterday the Humble Bundle 15 because all its games are available for Linux.
The problem was that while trying to install one game, my system warned me that I was running out of space.
Fortunately, I have a lot of unallocated space on that hard drive...at the end of my seven partitions. (Yes, seven! And I use each one of those systems!)
I decided to move some of the unused space to my gaming partition, but to do that I had to move 5 partitions to the right...and among those was the partition that loads GRUB.
Last time I did something similar, I messed up GRUB and my laptop would not boot; thus, I tried to be more careful. I replaced my current GRUB with the one of the first partition. Then, I moved the empty space to the left, one partition at a time, until it was next to the partition I wanted to enlarge. I then resized the partition, but I did not use all the unallocated space (just in case). Finally, I replaced GRUB with the one I had before starting the whole experiment.
Fortunately, everything worked. I understand that was a risky operation and that seasoned users would have a lot of much better methods.
Well, even if I am not so experienced, I could find a way to do it, and that makes me happy! :)