How do you change the font face and font size used by the Windows Ribbon Framwork's UIRibbon?
The font used by the ribbon does not match the font the user has chosen as their Windows preferences (which is the preference my application uses). This means that as the font in Windows gets bigger, the ribbon gets smaller.
Notice how the ribbon gets smaller in each screenshot:
Since the Windows Ribbon Framework is what the MSPaint team uses, I'm afraid you're stuck with the same problem as they are.
Anyway, If your customer has high resolution and have trouble seeing the fonts, the
correct way to fix that is to change the DPI settings of windows from 100% to 125% or 150%. This will scale all the fonts, including the ones in the ribbon.