It is not difficult. However, when I remove the original nozzle, I replace it with an E3D V6 nozzle. Why? Because the V6 nozzle is longer and seats against the heat brake inside the heater block rather than seating against the bottom of the heater block. This is the same way the E3D is assembled. For me, it makes it easier to swap nozzles because I don’t have to worry about how tight the nozzle is against the heater block. There have been many nozzle fractures on the Hexagon due to the nozzle contacting the heater block.
To R&R the stock nozzle with an E3D nozzle, heat the hotend up to a temp that softens the filament but doesn’t make it runny. I use 160 - 170C for PLA and ABS. That should work for PETG as well. Find an open end wrench that will fit the heater block and the nozzle. Hold the heater block with one wrench and turn the nozzle with the other. It is standard thread. Install the new nozzle at the same temp. Just snug the nozzle against the heat brake. Take care to not over tighten. Heat the hotend to printing temp and snug the nozzle again. That is it.
There is a guide on this forum to replacing the Hexagon nozzle. I will defer to that guide for that nozzle… I don’t use hexagon nozzles on any of my printers. https://forum.lulzbot.com/t/howto-change-hexagon-hotend-nozzle/2613/1
If you break something while replacing the nozzle, Lulzbot may or may not void your warranty. Modify at your own risk.