How do I upgrade my MacBook's RAM from 4GB to 16GB?

If it’s a Mid-2012 non-Retina MacBook Pro 13-inch Mid 2012, you’re in luck, it uses standard DDR3 SO-DIMM slots and supports 16GB (2×8GB) 1600MHz DDR3 just fine. In that case, you physically remove the bottom cover, swap both RAM sticks, and you’re done, no firmware tricks needed. But if it’s a Retina 13-inch (Late 2012 or newer) MacBook Pro 13-inch Retina, the memory is soldered to the logic board and there is zero upgrade path, regardless of what’s installed now. Don’t rely on what macOS says, click Apple menu > About This Mac > System Report > Hardware Overview and check the Model Identifier (e.g., MacBookPro9,2 = upgradeable; MacBookPro10,2 or newer = soldered).

What this really means is, confirm the exact model first, because on these machines it’s either a simple 10-minute hardware swap, or physically impossible.

If the non-Retina version, video RAM install instructions are here:

https://eshop.macsales.com/installvideos/macbookpro_13_unibody_mid12_mem/

HOWEVER...

Why do you want more RAM?

If the computer is slow, RAM is likely not your issue but rather the slow factory mech hard drive Apple used in those models. I have a 2012 13-inch non-Retina Macbook Pro that came wit 4GB RAM and I have upgraded over the 12 years I've owned it as a experiment Very telling results:

How about a big helping of test data from my 2012 13" Macbook Pro? Here are data on app launch times for my two slowest-to-open apps as I first doubled the RAM, then upgraded the slow factory hard drive to an inexpensive SSD, then double the RAM again

—Base system as shipped:

4GB RAM and slow SATA 3 GBps 5400rpm hard drive: Office and Photoshop Elements took 15-18 seconds to be ready to use.

—First upgrade, double the RAM:

8GB RAM and slow SATA 3GBps 5400rpm hard drive: Office and Photoshop Elements took 15-18 seconds to be ready to use.

—Second upgrade, inexpensive solid-state drive

8GB RAM and fast SATA 6 GBps SSD: Office and Photoshop Elements take under 4 seconds to be ready to use.

—Third upgrade, double RAM again:

16MB RAM and fast SATA 6 GBps SSD: Office and Photoshop Elements take under 4 seconds to be ready to use.

So what made the biggest difference?

A simple test:

— Is the computer is slow to boot?

— Are big apps slow to launch?

— once launched, do the big Apple seem to run fine?

Three "yes" answers scream "slow storage," not "starved for RAM."

Given the sky-rocketing costs of solid-sate storage today, it is not worth the trouble, The OWC "kit" I used to upgrade mine to SSD was about US$80 a year ago; today it is US$180.

If you have a 2012 model, click here and follow the instructions. The RAM on a newer one is soldered to the motherboard and not upgradable; while this also applies to some 2012 units, they all came with at least 8GB.

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OWC/MacSales is well ahead of the curve all things Mac

If you are looking for a source—

https://eshop.macsales.com/item/OWC/1600DDR3S16P/

See all OWC/MacSales partners/ reseller around the world:

https://www.owcdigital.com/reseller/resellers

16GB is the maximum recognized by your old workhorse— a very sweet machine if this is the mid-2012

13" MacBookPro9,2 or 15" MacBookPro9,1

Catalina macOS 10.15.8 is the latstes macOS it is capable of running

FWIW, I would not spend any money upgrading the RAM on a vintage/obsolete computer.