How do I adjust the thickness of the cheese slicer?

You only need to adjust the blade once. There are two screws on the underside of the slicer that you can loosen by hand. Push the blade forward until the slices are exactly as thick as you want. Then straighten the blade and tighten the screws. This will lock the blade and your slices will always be the same thickness.

It's best to leave the blade adjusted like this afterwards. That way you don't have to do it again every time. Just be careful when cleaning and putting it away that you don't cut yourself.