Who is requesting the termination of the lease?
In general, if you write out an agreement yourself that addresses the who, what, when, where, and why, then you will be okay. Both parties need to agree to its terms, and sign it.
It should say the lease dated August 1, 2008, between X and Y for 1233 That St, My Town, is terminated as of May 14, 1935. Specify what is going to happen to the damage deposit, and any arrears that may exist.
Hope this helps.