First time I had to do this I was terrified. After the first time, its no big deal. Consider purchasing a second vat that is ready to go so you can still print while you are replacing the other vat's FEP.
Some tips:
Search for a video for replacing the FEP on YOUR MACHINE. Follow it if you find one- likely out there. Some suggest having a bottle cap in the center when sandwiching the FEP in the FEP frame (my mono-x needed this)
Go to your local Hardware with the fastener bins and buy some replacement screws, just in case one goes into never land, and they are most certainly metric threads.
Buy a set of ball type allen drivers- using a 90 degree allen wrench is a recipe for putting a hole in the new FEP. Wiha makes a nice set if you don't already have one:
https://www.homedepot.com/p/Wiha-Precision-Ball-End-Hex-Screwdriver-Set-Inch-8-Piece-26490/337978127?source=shoppingads&locale=en-US&srsltid=AfmBOooDbSIMLu9CBfYmK-PdlvIUs1Q_zH2W7To2KqrwYhad027nQK-MC8oWhen you remove the old FEP, clean all the frames well.
When you tighten the screws, tighten halfway while using the same logic a tightening wheel lug nuts, i.e. opposite, back and forth. I always start in the center of the long sides, then move to the center of the short side, then the corners then toward the centers, repeat the sequence again for the final tightening.
After tightening you have to trim the excess FEP away. Go slow and use a sharp knife. I slipped and had to redo it several times.
ALWAYS re-level the build plate after replacing the FEP, even when switching vats. I re-level the build plate right on the FEP now, this way thickness does not matter. After all, the build plate contacts the FEP on the first layer anyway.
These are my observations, and good luck!