Place your cursor over the upper right of the chess board, click-hold the double-sided resize icon and drag left to make it smaller. Or right if it is smaller than the max, to make it larger.
Unless you have previously changed it, it should default to the largest size based on your system configuration (screen size and menu placement for daily)
There is also an option of Focus Mode in those icons that will get rid of the sidebars and make the board a little larger.
Hello!
I can't find in the settings where to change the board size. This option seems missing. Can I change it anyhow?