Want To Move Out of My Student House HELP

hi guys, so basically to cut a long story short i renewed another year and signed contracts to live in a student house next year with the same people i currently live with now. However, I've changed my mind and really don't want to live here in the academic year 2010/2011.

I'm really confused as to what to do now. I've definitely made up my mind, but how do I go about finding a replacement housemate? Will it be easy or an impossible task?

I am also wondering whether to tell my housemates about this decision before or after i find a replacement housemate? either way, my landlord says my housemates need to agree to the replacement housemate, and if they don't i will not be able to get out of the contract. HELP.