Even if you plan to move at the end of your lease, it is a good idea to notify your landlord 30 days in advance. If you want to leave before your lease is up, you need to come to some sort of agreement with the landlord. You should give the landlord written notice of your intention of leaving and then try to get a written acceptance. A written agreement will bind the landlord and enable you to leave legally. One option in negotiating leaving is to find someone else to move in.
Some landlords allow subletting.
Talk to your landlord about this possibility. As a tenant at will, there are two ways to terminate your tenancy. You can end your tenancy by agreement with the landlord in writing. If you can't get a written agreement, then make sure that you have a witness present when your landlord verbally agrees. The other way is to give your landlord written notice at least one full rental period before you want to move.