When you play Slingo® Casino or GameHouse Slots on your computer via Facebook, the size of the game itself is fixed within the window that Facebook provides to host the game.
But you can change the screen resolution of your computer monitor to make the overall image larger. It's not possible for us to know which screen resolution will be best for you, so we encourage you to try different settings until you find the optimal size.
If you need help with changing the screen resolution of your computer monitor, please refer to the article linked below.
http://windows.microsoft.com/en-us/windows7/change-your-screen-resolution
(Please note that the above instructions apply to Windows 7 PCs. For other versions of Windows, you should be able to right-click on your desktop and choose 'Screen Resolution' from the options presented.)