For the normal DIY-er, this is a really bad idea. The OLED display is fused to the digitizer and it requires extremely specialized tools and expertise to separate them, then re-fuse it to a new digitizer. There are services available on eBay that will do that for you for around $70 USD, making it a much better idea than trying to do it yourself.
Apple watches are notoriously non-repairable; the general consensus is that only the battery, force touch sensor and full display are repairable by us average joes, no matter how skilled we are at fixing things.