I needed to rename a SVN branch, so I did:
$ svn move https://server/repos/myrepo/branches/oldbranch \\ https://server/repos/myrepo/branches/newbranch
If you had simply wanted to rename a SVN branch in Eclipse, the easiest would have been to go into the SVN Repository Exploring Perspective, and then right click on your branch -> Refactor-> Rename