I have done the same there. Cash in lots of freerolls to build my bankroll. I recently got all of the info about cashing out freeroll winnings, and know what you need to do.
First of all, the site wants you to make a minimum deposit, and roll it over once before you can cash out. The minimum deposit is $50. You have to then play this $50 is either the casino or sportsbook. (not in poker) Once you have played this $50, you will have access to cashing out your freeroll winnings.
As far as actually cashing out, you have to verify your account info and identity with them. You need to fill out, then fax/scan their account verification form. You will need to photocopy your ID and debit card, if you want it deposited directly to your bank account, and include these copies.
It should then supposedly not take long to receive your cashout. This where I am not sure. I have yet to actually do it. Once I discovered what I needed to do. I put it off for a little while until I had more to cashout. They do charge fees for cashing out, but offer one free payout per month. So I wanted to wait to cash so I wasn't doing it twice.