When you first go into Rockstars Live and are in the Home area select Bank from the right hand column, which is directly under My Profile and above Therapy. If you play a number of other Storm8 games then you are going to find the Rockstars Live Bank familiar. If you have not deposited any money in the Rockstars Live Bank you will simply have a text box for depositing funds, but if you already have a balance then you have text boxes for both withdrawal and deposit. The top of the Rockstars Live Bank display will list your Bank Balance; below that will be the withdrawal text box.
If you want to either withdraw or deposit you just enter the amount you want into the appropriate text box and hit the Withdraw or Deposit buttons, respectively. You entire free cash amount will automatically be entered into the Deposit Amount text box, so you may want to change that if you do not want to deposit all of your money. There is a ten percent fee taken out of all deposits to the Rockstars Live Bank, though withdrawals are completely free.