How do I replace the showerhead holder on a Triton i90?

Replacing shower hose (cracked) and showerhead holder (also cracked) - the hose is easy enough obviously but how do I loosen the clam-shaped ends (either end) to allow me to release the bar and replace the showerhead holder by sliding off the old one and sliding on the new ? I don't want to force the ends for fear of cracking them and I'm sure there's a simple solution or knack to doing it - appreciate any assistance......thanks.