The intertnet is full of blog posts how to change the SVN password in Eclipse or Zend Studio. Unfortunatelly nothing I found on the interet worked. I've deleted the eclipse .keyring file and deleted the svn.auth folder.
Suprisingly the solution is really simple:
1. Change the perspective to "SVN Repository Explorer".
2. On the repository list right-click on the repository and then click on "Location properties..."
A dialog will popup, and right on the first popup you can change your SVN username/password combo.