Are you using a laptop or a desktop with separate monitor?

There is a sun burst on the key you use if a laptop. (each brand has a slightly different keyboard I think).
If you click "help" at the top of your window, and type in "adjust brightness" they will tell you which keys to hit.

If you have a separate monitor, the adjustments are usual on it and not the keyboard.

Are you using the default white and blue skin here? There is another called Spring, which is buff and cream and light gray green. You find the skins at the far lower left of the window.

I use the Spring because of my eyes too. It is very easy to read.