Here are the steps for changing the clamp:
a) unscrew the two screws underneath the clamp
b) load the clamp down, remove the cover
c) Pull out the metal strip in the middle, that is for holding the clamp down tightly
d) After that, pull out the two metal rod hinges at both top corners. To get them out, you have to slide the metal rod towards the center by using a pliers
e) Now, load the clamp up, when loading, hold it carefully giving it support
f) Carefully remove the whole clamp from that hindge like below
g) After that, you should can remove the whole clamp out. And you will only left with the loading arm
h) To fit a new clamp, just undo the steps, and that will be done.
---If you still find unsure on how to change the clamp, I can try to upload some more photos so that you can understand.
Hope my guide can help you a bit....