How to get keyboard marks off screen?

I’ve got an older Macbook, which I’ve had for 2 years, but is actually about 4 years old, and it has recently started to develop marks from the keyboard on the screen, probably because I carry it in my backpack for about 8 hours a day.
It’s not really that big of a deal, but I like to keep my computer at a low brightness and they can be pretty irritating.

So does anyone know how to get these off?

I’ve also heard reports from people with the same issue that Apple will actually replace the computer if they are scratched on (which they very well may be).