I think there is no mistery on this. You can click PREMIUM tab, then DEPOSIT/WITHDRAW button and this box will appear:



Just make sure to pay attention to the warning message and there shouldn't be any issues when depositing your FUN in freebitco.in.

100K FUN tokens will give you access to the 4th tier of premium program, which rewards up to 10 daily WoF spins and 10% extra APY on your bitcoin balance. Going this far, it should worth to think about acquiring more 25K FUN tokens, so you can have access to the 5th tier of the program.