
I guess it's the same as changing a rubber strap on Seiko dive watch or on a Casio G-shock. You'll need a penknife. Carefully slide it in between the case and the band until you feel it reach the spring bar (the band looks like rubber/silicone so there'll be enough flexibility to do this). Then gently twist the knife so as to push the spring bar end out of the case. Then gently pull that side of the strap out of the watch.
Always a good idea to put some tape over any areas you dont want to scratch and always use as little force as you can get away with.
(And good luck finding the springbar when it pings out, hits you on the forhead then ricochets to the other side of the room...)