How do I replace the speakers in my MacBook Pro

Those are not user replaceable parts. If the speakers are not working after updating Applications -> Utilities -> Audio Midi Setup utility settings, and no external audio is attached, then using external audio may be advisable either via Bluetooth, or RCA jack connector.

[Edited by Moderator]

If the speakers are not making sound, replacing them might not fix the problem.

Refer to Get help if the internal speakers on your Mac don't make sound - Apple Support.