Most cases of burn-in are just temporary and essentially just fix themselves over regular use. However, if it's significantly worse than standard burn-in and it seems to hang around, there are many different programs that "flash" your display in an attempt to remove the burn in. I would personally recommend jscreenfix:
http://www.jscreenfix.com/
Post back if this helped remove the burn-in, I'd be interested to see if it does.