the Gran' Sport...Compressor...Geophysic bracelet. I assume it has the summer/winter adjustment on the clasp?
I do hope the way to switch it isn't the same as a Michele watch (JLC is too classy for that). Can you take a picture of the back of the watch, where the bracelet attaches?
Personally, I've hoped JLC would implement the "Compressor-type" band change, as it is very secure. (I realize that not all models have the thickness of shoulders required to make it work.)
-Dean