You could do that at any time to be honest. You could give them 30 days written notice of a change in contract. Set a 7 day time limit for it to be returned and 30 day notice for the changes to commence just so you aren't left wondering whether they agree to the change and are staying, or they are leaving. Also include in the notice that should you not receive the notice returned and signed in agreeance by said date, that you will take it as their two weeks notice. You don't need to wait a full year and put up with something that does not suit your business needs for all that time. If this is a spot for September why don't you just return the deposit now and not start with anything and then advertise the spot as a 5 day spot. There is still plenty of time to fill it for September.