Manual

Go to the Update tab and click on the link to update from firmware file.
Upload the latest firmware and wait for the robot to be updated.
Update over USB-C
Download the latest firmware from http://edu.irobot.com/create3-latest-fw.
Copy the firmware to the Raspberry Pi:
sudo scp ~/Downloads/Create3-G.X.Y.swu ubuntu@xxx.xxx.xxx.xxx:/home/ubuntu/
SSH into the Raspberry Pi and update the Create® 3 firmware over USB-C:
sudo create_update.sh Create3-G.X.Y.swu
or
curl -X POST --data-binary @Create3-G.X.Y.swu http://192.168.186.2/api/firmware-update
This may take a few minutes.
Debian packages
Debian packages can be updated by calling:
sudo apt update
sudo apt install <PACKAGE>
For example, updating the turtlebot4_desktop package can be done like this:
sudo apt update
sudo apt install ros-galactic-turtlebot4-desktop