OK, follow along below....
In order to delete personal templates, you have to be able to gain access to your user library folder which is hidden by default in Lion and Mountain Lion. If you're using either of those versions, you need to do this first.
Open your Terminal application (Applications, Utilities, terminal.app) and type the following at the prompt:
chflags nohidden ~/Library/ and then press enter. Now type in the word exit and press enter. (You can copy and paste from here.)
Your library folder should now be visible. Open your Finder and navigate your way here:
Macintosh HD/Users/your user name/Library/Application Support/Microsoft/Office/User Templates/My Templates/
All of your personal templates will be located there. Just remove those you no longer need.