To update a system

sudo apt update

sudo apt full-upgrade

sudo apt-get autoremove

sudo apt autoclean

Or all in one

sudo apt-get update && sudo apt-get upgrade -y && sudo apt-get autoremove && sudo apt-get autoclean

sudo reboot after the update to have all including new kernel started. if the file /var/run/reboot-required exist then a reboot is necessary

cat /var/log/apt/history.log shows when last update has been done

sudo shutdown before removing power would be the clean way

sudo df -T to check memory size of the SD card

sudo apt-get clean do remove temporary files from the SD card