need help upgrading ubuntu 10.04

I origionally had Ubuntu 9.10 (i think) on 2 of my machines.
I upgraded both to Ubuntu 10.04 quite some time ago.
this upgrade went fine.
however, I am trying to upgrade to a more recent version (I think they're on 11.10 now)
however when I open the update manager there is no option to upgrade to a new version.
my system is up to date as of 6 hours ago...
I am at wits end trying to figure out why it wont let me upgrade when I know the system is out of date.

I also tried the terminal command: do-release-upgrade
and it told me that there are no new releases.
can someone tell me what I am doing wrong, or what is wrong with my system?