[ubuntu] Updating from 10.10

I have an old laptop running Ubuntu 10.10 that I've just picked back up. I want to update it to 11.04 in order to be able to update it beyond that, but I'm havign a lot of problems with it.

When I 'Install Updates' in the Update Manager, I get:
Requires installation of untrusted packages

The action would require the installation of packages from unauthenticated sources.


When I change the server from the main server to another, there are no packages to update at all.

Any ideas?