Upgrading WordPress

I am sure this question has been asked so many times and reading the forums I find many people with weird issues that I would never want to tackle myself. I have searched for a blog or something on this topic but unable to find anything.

Can anybody point me to a tutorial or blog how to upgrade from say version 2.5 to the latest version of wordpress without getting it all messed up

last week I moved a couple of my blogs from a sub domain to the route directory simply by exporting the content out of the old version and then importing it back into the newly loaded version. It worked perfectly. Is this the best way or is there another simpler way.