I am having this set up at the moment :
and I would like to give the unallocated space between
/dev/sda4 to /dev/sda5`. How can I do that now ?
There are some steps you must follow:
You have to do this on a live CD, unmount all your partitions, including swap, and do it in steps. Right now sda5 and sda6 are mounted, so you can not work with them.
From a live CD, first unmount all your partitions (you can do this in the gparted menu).
Then, in steps, -> Increase the size of sda4 -> apply changes -> increase the size of sda5 -> apply changes.