How do I change the board and/or pieces? (BlitzIn)

Menu above: Edit > Settings > Board/Pieces Tab. 
Under 'Style' you can choose with the V button the different options for board and pieces.
 

The Board/Pieces tab also gives you display, animation and time settings which you can turn on or off. 
These include: Highlight Moves, Show Captured Pieces, Examine Palette, Material Count, Board Console, Flags, Mugshots, Low on Time Warning, Animation speed, etc.