If you want to remove OOTP from one of your computers, you should unlicense it first or else you'll tie up one of your activations on a computer that's not even being used to play the game. Here's how to unlicense:
OOTP 11-15 (PC/Mac, Linux):
- Open up the game and on the very first screen that comes up, click on the preferences button.
- Next, click on the license tab.
- Finally, click "release license / unlicense game"
OOTP 10 and earlier (on a PC), do the following:
- Right-click the game icon and choose "properties" at the bottom.
- In the "target" box, add a blank space and then "-unlicense" without the quotes to the end. For example, if it says "G:\OOTP X\ootp10.exe", then change that to "G:\OOTP X\ootp10.exe" -unlicense.
If the game is not installed for you to unlicense it or if the above doesn't help, open up a support ticket.