For extending the simulator itself you'll need developers access to the cvs repository. Ask for it by using the appropriate procedure on the AGV Simulation SourceForge website. Please only submit code to the repository that completely compiles, works and has been tested.
For thesis students: first ask your assistant if developers access is really needed. If you get developers access and your are planning to make an extension, please make a new branch for this extensions and use the appropriate package names. Ones the extension is considered to be stable, it can be merged with the HEAD branch of the repository.
You'll need to checkout the projects you want to extend using your SourceForge account details (see SourceForge website for more information about obtaining an account).