Try hitting CTRL plus the "+" sign on your keyboard. That should make it larger. I use a MacBook Pro and it's the Command key and the + sign and it's been a while since I used XP but I think it's CTRL +
You can also change the size of the board in your live chess settings but it doesn't sound like that is your problem because I don't think any of the size options in settings make the chessboard as small as you are describing. Hope this helps.
The board is tiny, as if it is sized to be on a smart phone. The last time I played, it was much larger. I can't find a way to change the size. Any ideas? [XP professional, have made no changes in settings]