Simple. You don't.
I'd hazard a guess and say you are trying to access Bebo et al from a PC which belongs to someone else.
I'd also hazard another guess that you are trying to do this to the school's computers.
Firewalls (and other means of restricting access to luser sites) are there for a very good reason. They help to prevent undesirable things getting into a PC when people (usually of low intelligence) blindly access parts of the web which are best left alone and who can't restrain themselves from clicking wildly on tainted links.
If you want to compromise a computer, please do it to your own. not that belonging someone else.
You may also consider actually learning about just how much damage you can do to a PC by placing it at risk.
You may like to read this:
As a followup you may just like to do a comprehensive sweep of your own PC.
Don't just do so with antivirus software, but a proper sweep which covers trojans and rootkit infections etc. Go to www.whatthetech.com, especially if you use it for accesssing sensitive things - like your hotmail account, paypal, banking, etc.
Check out the infections forum, download and run Hijackthis and post the log file on a whatthetech.com forum
Don't use your PC for anything sensitive until you get the all clear.
In an extreme case, it may be suggested that you reload the operating system before you can rest comfortably.
Please, spend your time at school getting at least a little education. I'm tired of meeting fresh faced kiddies who have had a cushy time at school, suddenly realising that in the real world, their atitudes and their assumptions about what their "rights" are, aren't worth a light.