Be very careful here. Please do not take my views as gospel - I would hate to lead you in the wrong direction

- but for what it is worth..... I am not sure if all sets are the same but mine had instructions on taking care of the screen and surrounding piano black (white gloves were provided with the set!). Use a clean warm slightly soapy damp cloth to clean and avoid at all costs Benzine or alcohol based cleaners or anything in a spray as these can damage any anti-reflection coatings on the screen.
For serious marks - contact your supplier (etc etc)
Cheers