How do I get my security deposit back?

I don't think you will get it back if you are breaking your lease. It is a "Lease Agreement", which is a contract in of itself. Even if you write a letter with your request, it is up to your current landlord to grant your request, plus give you your security deposit back. I found that if you speak with them, and tell them your situation, but make it sound really good, and also tell them you will return your rented home in perfect condition, and also let them know if they need any work done to your rental before you leave, you will happily do it (painting/sprucing up...), so that hopefully you can regain the whole deposit from them, then alot of the times landlords are willing to help. Now is the time to kiss up and do what you need to do to get out.