To copy or combine entire boards, first go to Settings > Boards and press on the "+" button to add a new board.  From the dropdown menu, select "Copy or Combine" 

Copy or Combine boards in Bitsboard

Next select the boards you would like to copy or combine.  Voila.  You are all done.  You can copy a single board or combine and merge multiple boards into a new board by using "Copy or "Combine."