The layout can be a bit complicated. Many of the Cells have more than one Property Set which are used to display the Cell's contents at different times during the tournament. When you change the attributes of one of them, you have to make sure you're changing the one that is currently being used in the Game window or else you won't see any change. Best thing to do is change the attributes in all of the Property Sets of the Cell. Make sure you click each of the Property Sets on the left side of the Cell Properties dialog and change the font to the desired size. Then press OK.
Another thing to try is to enable Layout Scaling. On the Layout tab, press the Preferences button, then check the box next to "Enable layout scaling". Then check the box under it that says "Use optimal resolution setting of the current layout". This can produce a better looking layout at higher resolutions.