First you will need to navigate to System > Administration > Software Sources. A window will come up like the one shown below.
Software sources window
You will now want to navigate to the Updates tab. Then in the Release Upgrade section in the drop down menu you will want to select Normal Releases. Then you can hit the close button.
You should have Normal Releases selected
Now you will need to navigate to System > Administration > Update Manager. You will need to click on the Check button and install any new updates (if you have any) then click the Check button again and you should then see a message that says New distribution release'8.10' is available. Now you just need to click on the Upgrade button.
8.10 upgrade screen
You will then just need to follow the on screen directions to complete the upgrade. Now you have upgraded from 8.04 to 8.10 in a very simple and quick way. So go have fun with you new upgrade of Ubuntu.