How can I take apart the handset to change the battery or microphone

How can I take apart the handset to change the battery or microphone

People have a had time hearing me using the GE 2-9220 NIC handset. How can I take apart the handset to either change the Lithium battery (which it apparently has) or change the microphone? There are no obvious places for screws. There are internal catches at the bottom near the cord.