Display on screen - adjusting size

I have glaucoma. It is under control now, with the help of eye-drops, but I have lost some vision. I experimented with changing the settings on my computer - going through Control Panel and changing Font Size. Yes, it's nice and big. Too big. So big that I can't find my way round the screen without endless scrolling and getting lost.
So, I need to change it back to the way it was. Yep, can find my way back to Control Panel, can put settings back to Small Font (or to custom size). But I think there may be an Apply Button. All it will let me do is close the window, no Apply Button. It's possible that it's so large that it's gone off the screen. Heeeeeeelp!!!!!!