how to install a firmware on at&t r800at play?..

[pctek]

I have a xperia play 2.3.3 r800at at&t model and I would like to install a r800a generic 2.3.4 north america Im assuming generic means a vanilla no bloatware firmware to the play.

I have the 2.3.4 firmware but what program and the steps to install it? The play is unlocked so will it stay unlocked? thanks