It's quite simple!
To add a new payment method, go to the homepage, then select: Menu > My Account > Deposit Funds > Add Method and select the method you would like to deposit with. Following these steps, you may then enter all the relevant details in the boxes provided.
A new payment method can only be registered if your account balance is below $100.00 and you have no pending withdrawals.
Please note that a payment method can only be registered to one playing account at a time.