To update your Model Maker complete the following steps:
1) Download Model Maker from here: Model Maker Full Demo
2) Quit Model Maker if it is running.
3) Run the downloaded file and install Model Maker.
4a) Windows XP: Place the setup file that was send to you, in your Documents and Settings / (Username) / .MMSystems folder.
4b) Windows 7 / Windows 8: Place the setup file that was send to you, in your Users / .MMSystems folder.
5) Run Model Maker