To update your your settings or change to a newer branch of marlin you will need to use a software package called visual studio code, As i have used klipper on all of my printers for many years i simply cant remember the full process so i will embed a tutorial video to show you how its done.
Download Visual Studio Code – https://code.visualstudio.com/download
Downloading Marlin firmware – https://github.com/MarlinFirmware/Marlin/tree/bugfix-2.1.x
or direct from marlin firmware – https://marlinfw.org/meta/download/
Updated Marlin firmware setup guide – VS Code and Auto Build Marlin – Teaching Tech
MARLIN – Essential Guide To Start Editing Your Own FIRMWARE – ruiraptor