Another Don
121
It's a piece of cake, provided you have a good springpin tool...
The replacement strap should be 19mm wide at the lug ends tapering to 16mm wide at the buckle/clasp end. The strap is attached to the watch with springpins. Attack these from the back of the watch since the apron on the front of the case partially obscures the pins.
The clasp is attached to the buckle end of the strap with a third, shorter, springpin. There are holes in the edge of the clasp which make attacking that springpin fairly easy and straight forward. The hard part will be getting that springpin re-seated with the new strap. There's not a lot of wiggle room and if your chosen replacement strap has a thick leather, it may take a little time to get the springpin centered under the hole so that it will snap into place.
But the entire process shouldn't take you more than about 15 minutes.