
The iFixit Mac Laptop Repair guides provide excellent step by step instructions for SSD replacements specific to each model. Make sure you have the right equipment for performing the upgrade. These are the 2 machines I updated, named for Futurama characters.

has thorough descriptions of each model, use About This Mac-> System Report to gather up all the details of your system. Take the time to figure out exactly which model you have before getting starting. The total cost was under $90 USD each for upgrading to 500 gigagbyte drives. Go read at least the first page of that thread if you have questions I don’t answer, there are 220 pages of feedback so far. There is an amazingly thorough thread on this, but I figured I’d post my experiences upgrading 2 of my laptops that I’ve upgraded so far.

Relatively recently (10.13) it became possible to upgrade these systems with an aftermarket adapter and stock NVMe M.2 form factor SSDs. The SSDs used by MacBook Air and MacBook Pros shipped between 2013-2017 used a proprietary adapter. Apple laptops are somewhat notoriously resistant to upgrades.
