Applications :: Delete MS Office From Computer And Reinstall?

My son installed Microsoft Office on his computer and he used the same serial number as the one on my computer. Now every time he uses office I have quit it form my computer and when I need to use it he is quit his office.

Well, we have student teacher copy of office with 3 serial numbers. I have 2 other serial numbers that he could have used. Is there a way to wipe the serial number he entered on his computer and use the other serial number? If not how could I totally remove office from his computer and install it again with a new serial number.