HELP!

Hello, I am new at this and not very good at using the iMac that i have. However i have a few questions. I just download OS X Mavericks and now my iPhoto won't open. Will updating it fix this problem? If not, how can I Uninstall OS x Mavericks? I cant get my built in camera to turn on or be recognized on imovie now either. HELP!

Lia