Each prank has its own unique way of stopping itself. For specific instructions on how to stop a particular prank, please see that programs documentation. However, almost all pranks can be stopped by rebooting your computer.
Alternatively, you may email the developer/company for support. You will find a link to their email address on the program information page.
PLEASE DO NOT email us asking how to close each prank. We do not create these pranks, we only display them in our archive.