Learn how easy it is to sync an existing GitHub or Google Code repo to a SourceForge project! See Demo
From https://sourceforge.net/p/jedit/admin/ or else from
https://sourceforge.net/p/jedit/admin/tools I seem to recall there was a way to manage the members of the project. I can't find it now.
I also can't see any way to leave a project.
I believe the page you're looking for is Admin -> User Permissions (in the left sidebar).
It is not currently possible for a user to leave a project, another admin (or SourceForge site staff) needs to perform that action.
Chris Tsai, SourceForge.net Support