Remove the 2 PH1 screws which retain the SSD and heat spreader. The innermost screw also retains the battery, you will have to gently lift the plastic battery mounting tab with your fingernail or a pry tool, allowing the copper heat spreader to be slid out from underneath.

The SSD is now free to spring up from the slot. Pull it in a straight line in the direction which it points at rest. Gently insert your replacement drive. Reverse the above steps to reassemble.