Is there any non-painful way to upgrade an Eclipse installation? I have tried browsing the eclipse site but I cannot find an useful description.
You can simply download the newer version, then use "File -> Import -> Install -> From Existing Installation" to add all the plugins you had in your previous installation.
Here's a link describing the whole process in details (it says "on Mac Os X", however it should work for other systems as well):
http://www.corephp.com/blog/how-to-upgrade-eclipse-juno-4-2-to-eclipse-kepler-4-3-on-mac-os-x/#.UfJsoI1_McY