Important! Currently the image upgrade is possible only via a clean install (via SD card). Running "sudo apt upgrade" would lead to unexpected results and problems! Avoid running "apt upgrade"!
If you decide to completely re-write the image on the on-board eMMC memory, follow the advice in the next section.
In order to just update it is safe to run "sudo apt update" Once Linux boots, connect to the Internet either via on-board Wi-Fi adapter or by using an Ethernet cable.You might use the graphical network manager or edit the configuration files via command line.
Then open a console terminal (press ALT+CTRL+T) and type:
sudo apt updateInsert your password if prompted and wait until the commands succeeds.