Welcome to the forum,
@bigroly. You've picked a solid upgrade to start your posting career with.
The HPR50 to HPR60 swap on the Fuel EXe is a well-trodden path at this point, and the good news is the motor is essentially a bolt-in replacement. The speed sensor and main wiring harness from your existing bike plug straight in, so mechanically it's quite straightforward. The main complication is the software side: the new motor needs to be activated via the TQ dealer service tool, and during that activation the software checks your frame serial number. Because your bike originally shipped with an HPR50, the HPR60 gets capped at 300W peak power rather than its full 350W capability. You still get the bump to 60Nm torque, the improved efficiency (owners have reported 15-20% better range with no other changes), better thermal management thanks to the cooling fins, and it runs a touch quieter. So even with the power cap, it's a meaningful upgrade.
One thing to be aware of: the HPR60's cooling fins may need trimming depending on your motor cover clearance. Worth checking before you commit.
On sourcing, the motors have been available through Silverfish (TQ's UK distributor) for roughly £800-900. Whether your Trek dealer can order one directly or whether you'd need to go through Silverfish may depend on the dealer's relationship with TQ. Either way, the dealer will need the TQ service dongle to activate the motor against your frame serial, so unless you fancy buying your own dongle and getting set up as a "dealer" yourself, you'll want a shop involved for that step. It's worth noting that a Trek/TQ service dongle without official Trek habilitation can only do firmware updates, not motor activation, so make sure whichever shop you use has the proper dealer access.
As for total cost including labour, I don't have a specific UK figure for the full operation, but the motor swap itself is relatively quick for a competent mechanic. I'd expect an hour or two of shop time on top of the motor cost. Ring a couple of Trek dealers and get quotes, as it'll vary. If anyone here has had this done at a UK Trek shop recently, do chime in with what they charged.