And if the model is on the teamserver then you have to download svn and use the SVN repo browser to change the model name on the teamserver.
You can go to home.mendix.com, click on your project, click "get project ID" (on the right), edit project settings and there'll be a field where you can edit the name. No torturesvn needed.
Have the Modeler closed. Find the .MPR file in your project directory and rename it. Then you need to browse to the new file in the Modeler when you want to open it the first time
Is it possible to put 'changing a project name' on a whishlist?