Wow - so much mis-information...

Tempdb will be resized to its initial size upon restart. If it has grown to 2GB over time - then that is the size it needs to be. If the initial size was set to 2GB, then changing the model database, shrinking the database, or any other options are not going to change this.

To change the initial size, you have to put SQL Server into single-user mode. Then, you can resize the files using SHRINKFILE with a new size. Once that is done, the initial size will be reset and when you restart SQL Server it will resize tempdb back to the new initial size.

Note: shrinking tempdb while users are accessing the system could cause corruption in your databases. It is not recommended and should not be attempted unless you can insure that no users are accessing it. That is why you need to put SQL Server into single-user mode.