Can I upgrade Ubuntu to 9.10 from 8.10, without using an ISO image?

"it's really non-geek if you follow the instructions to the letter. Fire up Terminal, and type the following line :

sudo apt-get dist-upgrade

There's a way with Synaptics, but trust me, this is waaaay easier.

EDIT : Missed out that OP wanted to upgrade to 9.10, which hasn't been released yet.

Do the above pre-edit answer first to upgrade to 9.04 (just to be safe). Then :

Type in Terminal

update-manager -d

Update Manager should open up and tell you: New distribution release '9.10' is available. Click Upgrade and follow the on-screen instructions."

"gd: update manager turning gray

I had the same issue upgrading to 9.10. Therefore, I first run all upgrades for my existing ubuntu version. I had to go through a couple of update cycles. This included an upgrade of the download manager.
After this, I could upgrade to 9.10 without problems."