I was trying to change to canvas size to fit my image in GIMP the other day. I gave up and almost threw my laptop out of the window.
Paste as a new layer next time.
Also the more you use it the more you get use to how its done in gimp. Some things are easier in paintshop but paintshop is not free.
If you know what tool does it helps alot as well.
http://docs.gimp.org/2.6/en/
Don't you mean photoshop? I mean paintshop is old now, and still only uses 16bit colors if I remember correctly. Then again the last time I worked on it was paintshop pro 9...