I accidentally exited the window asking me to upgrade to 12.10, and now I can't find a way to upgrade other than wiping my drive and installing the latest iso.
For a GUI version of Karthik's method:
When you are in Update Manager, click on Settings. Go to the Updates tab and change "Notify me of a new Ubuntu Version" from "For long-term support versions" to "For any new version". You will have to enter your password.
Then Close that window and click Check. It should notify you near the top that "New Release '12.10' is available" and have an Upgrade button.
This method works for any version of Ubuntu to the next version, at least since 9.04, likely longer. Keep in mind that doing an upgrade instead of installing fresh (with a backup of your home directory and any other data) always has the possibility of causing hiccups.
Have you opened the update manager? It allows you to update and upgrade the system via a graphical interface.
Install any security updates, then open Update Manager's settings.
Make sure your settings look the same as mine. Especially make sure that 'Notify New Ubuntu Version' is set to 'For Any New Version'. Then run Update Manager again.