Never, never try to delete a program, it needs to be uninstalled.
Sometimes there's an option to uninstall in the game folder, sometimes not; this method should work every time:
Open the Control Panel from the Start menu. Then choose "Uninstall a program" under Programs.
Now you will get a list of all programs installed on your computer; scroll down to The Sims 3 and single-click. At the top of the list there's an option to uninstall (maybe it says Uninstall/Change).
Click it.
It will ask you if you're sure, maybe if you want to keep saved games (I did that and it worked fine but you should probably do a backup anyway). Then it uninstalls. It probably takes a while.