If you plan to upgrade your Ubuntu 9.04 Operating system to new Ubuntu 9.10 you can do it via your "Update Manager"
like this.

1. goto System -> Administration -> update manager

then you will see a window like this.

Then click on "upgrade" button. Then you will see a window like this.

this will take some minutes according to speed of your computer.
At the end of this your  computer will restart and after that you can log with Ubuntu 9.10.
Thats all enjoy.
if you received an error message like following screen shot you should delete some Useless items and build up free spaces of your hard disk.
And re continue with these steps.