Jan,

There is no uninstall concept for Eclipse. Everything in Eclipse are a
composition of jars and plugins and they are all in the folder where you
unzipped it. For e.g C:\Eclipse.

If you want to uninstall and preserve your old work that you had in
workspace, just copy the workspace to a temp folder, delete the entire
Eclipse folder and you are done.

To install new one, download the new zip file, unzip it to the right
location and copy your old workspace over to this place. You would have all
your old stuff.

Suren