Can someone help me hack an invisionfree account?

So here's the deal, there's this guy and he's really stupid, and has ruined my invisionfree site. He has his own invisionfree site and I want to destory the site/cripple it. But to do so, I need to get into the Admin CP. And I need his password, can someone reccommend me a program or something that can help me accomplish this?

I am a complete MORON when it comes to hacking, so go slowly. I don't want to do anything complicated. Just hack his account/the admin cp to his website.

Thanks! :D