Yeah, go to account under the home tab, then to online chess settings and there's an option to change the size of the board.
Size of the board here

Sometimes depending on what internet browser you use it may not change the size of the board. I had that problem with internet explorer so i used chrome and i could make it bigger.
If you need help, please contact our Help and Support team.
Does anyone know a way to make the board almost full screen size? I used my computer's zoom, but then if I try to move the board to the center, the board changes to the size of a postage stamp. Then I'll reduce the zoom to start over, but then it reduces the board to the size of a politician's brain. Is there a way to make it fairly large and have the board in the center? Thanks