It is very easy. The grill comes off really easy by removing 9 plastic rivets, and four small bolts. Then starting at one side pull the grille away (there are clips that hold the grille in place) working across to the other side. It takes a pretty good pull to get it started from one of the sides by the side marker light.
This is a pretty good video, and I'm sure there are others: 2021 Base Ford Bronco custom retro grille painting - white with red letters - DIY - YouTube
The OEM letters have plastic posts that are melted onto the back side of the grille as shown in the video that need to be removed by drilling. Be sure to take your time and just go slow and use a drill bit of correct diameter, or use a Dremel, then drill. I used a really sharp wood chisel and chiseled the plastic welds off, then drilled with correct drill size: it was easier I think to use a chisel then be able to keep the drill centered and not make the holes any larger than what is there. Some of the pins will just push through if not melted to the sides of the holes. The new OEM letters have double sided 3M tape, and the plastic posts use metal push on clips to hold them from the back side, a really good set up. UPR Direct Replacement Grille Letters Compatible 21-23 Ford Bronco Carbon Gray | eBay
Hope this helps.