Don't. People usually complain (and have so more for 9.10) about upgrade problems... just backup your data/settings and do a fresh install for least hassle...
I would recommend you to stick to 9.04 some more while until you have problems in 9.04 or unsupported hardware. 9.04 was more stable for me but didnt have wifi support for atheros and the backported drivers were crap. 9.10 was a must in my case, well pulse audio is also more mature in 9.10
Bah i guess I am not much helping you to stick to 9.04
Ok, I am hijacking the thread here. But heck, I just installed clean. Things went fine without any issue. Found it a bit slick showoff, performance wise I couldn't figure out.
Right now my laptop is running 9.04 32-bit version and there are no issues. I have requested a 64-bit Server edition 9.10, lets see if that comes through otherwise gonna download it after my MW2 download completes. Will shift to 64-bit Server edition later then as my laptop is my Download rig, NAS, almost everything.
As for Upgrades, I know what u guys mean, I too had my Linux Mint and Open GEU installation gone FUBAR due to the online upgrades.
pidgin didnt support voice chat to being with, I removed it anyway in 9.04, empathy was much better for me. dont remember gimp being bundled in older default installation