In a joint rental lease, all persons named on the lease are responsible for paying rent and are liable for any damage that may occur. If a roommate decides to move, there will be a need to officially release this roommate from any future obligations or liabilities. Depending on the landlord or apartment association, this can be a difficult situation that might require legal counsel.
Discuss with those on the lease to ensure that it is OK to have the name removed. It is important that everyone on the lease is supportive of this decision in order to make the process smoother with the landlord. If the roommates do not agree with this decision because it would cause a financial burden on them, then offer to find a replacement before leaving.
Notify the landlord that the roommate wants to be removed from the rental lease. Some landlords simply request written permission from the other roommates, and then will remove the name from the lease.
Negotiate removing the name from the lease with the landlord if the landlord does not agree to only having a written permission note from the other roommates. This can include paying a penalty, which should be lower than your part of the rent for the remainder of the lease's duration. Another option is to agree to pay until another roommate is found to replace this individual.
Contact an attorney to find out if there are legal options that can be pursued. If the reason for moving out is due to either illegal or dangerous behaviour by other roommates, or the house has ignored requests to fix a problem -- then the landlord may be forced to remove the person from the lease.
Demand that the landlord put everything in writing, whether he or she agrees or disagrees with removing the name from the rental lease. Having all communications documented is important to prove that the landlord was OK with the roommate leaving, or it can possibly assist the attorney in making a case against the landlord.