Poker bonuses need to be ‘cleared’ before they can be withdrawn. This applies to no deposit bonuses too. To clear a bonus, you need to play through the total amount a set number of times. This typically ranges from 5x to 25x. You do this by collecting points at real money cash games and from paying tournament fees. Once your playthrough is completed, you can withdraw your balance.
Note that any other bonuses you are clearing will be stopped when you make a withdrawal.