The easiest way is you wait for them to leave then you put their stuff into boxes and leave them at the front door. Then change the lock. Inform the apartment manager that they will not be living there anymore and if they try to get in, call the police. Another way that is more fun is if you are on a month to month lease, give notice. Then when they are away, move out. They will come back to the apartment, will see that you are gone and if they stay there after the move out date, they are squatters. The landlord will then either evict them or give them the chance to rent the apartment on their own. Obviously you should not tell them where you are moving to. Lastly, you could just tell them to get out and see what happens.