How to replace the screen?

Daniel,

Looking into this I found several videos on YouTube of tear-downs for your watch, frankly none of the ones I watched were very impressive, but you can view a few of them to get an idea of the approach. I would NOT advise heating the screen with a lighter or using a razor blade to pry the screen up, as in a couple videos... but hey, you may like to live dangerously... Never mind, in general: Heat the screen to soften the adhesive, (IFIXIT has safer tools for sale if you wish to buy them but you can probably find appropriate substitutes) pry up the screen and replace the damaged one (I did find some for sale cheap, also screen protectors of various types and if the watch is showing it's age you might consider replacing the battery while you have it apart. Possibly the best of the videos I looked at is HERE. the only one that goes over putting it back together that I found.

Hope that helps and...

Good Luck!