I can't seem to upgrade to the latest version ubuntu. It asked me once, but I was doing something else at the time. Now that I ant to do it I can't find it. I can find software updater, but that just seems to update programs that are on the computer.
The update manager has the upgrade button you are looking for.
start the update manager with typing
Or you can search for it in dash by typing update manager.
Click on the Gear on the top-right corner> System Settings...>Software&Updates there go to the Updates Tab and then check that "Notify me of a new Ubuntu version is set to: For any version. then execute the Software updater and it should tell you (if not hit refresh) Hope it helps
Click Alt + F2 and type update-manager at the prompt or do the same in Terminal.
If this does not show the update open a Terminal window and type in
This searches for and upgrades your system
How to safely upgrade from an older Ubuntu version to a newer Is the best and safest way.
Edited with corrections suggested below