Menu above: Edit > Settings > Your Options Window comes up. Choose from the list on the left Playing > Under 'Move input' uncheck 'Auto promote queen'.
When checked you will automatically get a Queen when your pawn can promote
When unchecked, when your pawn can promote, you will get a pop-up window appearing in the middle of your board where you have to click on a Rook, Knight, Bishop or Queen.
When you have decided if you want ‘Auto promote queen’ on or off, press OK.
Alternatively you can keep Always promote to queen turned on but when you want to move a pawn to promote but rather have a Knight instead of a queen you use the command method.
Lets say you want your pawn to move to e8 and become a knight. Type on the command bar: /e8=N This will move your pawn to e8 and turn it into a Knight. (Knight = N, Queen = Q, Bishop = B, Rook = R)