[ALUG] Uninstalling Ubuntu and installing another Linux OS

I think the time has come. Yesterday 11.10 'uninstalled' Libre Office off its own bat. Nul points and a bit worrying. So, without wishing to turn this thread into a discussion over which distro to go for, and without installing it over Ubuntu which I'd rather not do, how do I swap? I've used Ubuntu for ages now so I've no idea who to go about this. Bev.