You can upgrade ubuntu 10.04 to its latest version 10.10 with the terminal like this...

1. goto Terminal 
Applications -> Accessories -> Terminal

2. now give the command
    sudo apt-get install update-manager-core

3. then give the next command
    sudo do-release-upgrade your system will check for new upgrades and will ask to upgrade..
 enter y for upgrade
 enter N for cancel
 enter d for the details..


If you plan to upgrade your system with the GUI (Graphical User Interface) you can do it like this..
1. open the update-manager
System -> Administration -> Update Manager

2. then you will see a message like  "New Ubuntu release '10.10' is available" then click on the upgrade button to do upgrade...


NOTE: if your system will not detect any new upgrades you should edit a file in /etc/update-manager/release-upgrades.  Read the next article "Problem with the upgrade ubuntu 10.04 to 10.10"