How to change boot camp partition if is set?
I am guessing your forte is not computers, this is not the best method, nor the fastest by any stretch; in fact it could possibly be the slowest way to do it. But it will work. 


boot into windows
start migration assistant and copy all your settings and apps and docs to an external HD 
Go back to osx
Delete w7 partition
run bootcamp assistant.
redownload the Windows Support files if you lost them (important)
choose new partiton size
reinstall windows 
reinstall Windows support (apple drivers)
run migration assistant again and copy all your settings and apps and docs back.


There are other ways to do it (buying Paragon Partition Manager for instance) but this way its slow but free and almost impossible to screw up your computer.