Gently wiggle the scroll wheel up and back to remove the scroll wheel from the mouse.
Use your fingers to simultaneously push the scroll wheel and its frame forward and pull back on the plastic tab directly behind the scroll wheel until it is loose.
Use your thumbs to pop the scroll wheel out from its plastic frame.
Upon reassembly, be careful to ensure the silver box on the side of the wheel is placed into the frame with the tab facing downward so upon entry into the frame it fits into its slot.
When reassembling the mouse, place the loose plastic piece that holds the scroll wheel and wire in place into the rectangular slots in the circuit board.