Amazon.com: Waveshare Accessory Compatible with Raspberry Pi 4 Model B 2GB RAM with Powerful Processor Faster Networking Support Dual 4K Output and Different Choice of RAM Comes with a Copper Heat Sink :
Raspberry Pi 4 (8GB) Tested: Double the RAM, New 64-Bit OS | Tom's Hardware
Raspberry Pi RAM Upgrade By Replacing SMD Chip | Elektor Magazine
5 Major Upgrades on Raspberry Pi 4 Model B
Can I Upgrade the RAM of Raspberry Pi
Official Original Raspberry Pi 4 Model B 4GB 8GB Development Board Kit RAM Core CPU 1.5Ghz 3 Speeder Than Pi 3B+
I made the Raspberry Pi 4 with 3GB of RAM. : r/raspberry_pi
Raspberry Pi 400 Gets an 8GB Upgrade — By Hand-Balling and Soldering a Donor RAM Chip - Hackster.io
Raspberry Pi 400 Gets an 8GB Upgrade — By Hand-Balling and Soldering a Donor RAM Chip - Hackster.io
Raspberry Pi 4, Now With Upgraded RAM & A New Price Point!