Update Server Software
The easiest way to update your SlickStack LEMP stack is just to run sudo bash /var/www/ss-update which uses the built-in apt update and upgrade commands in Ubuntu. You can also run those commands manually if you prefer, and it should not affect any of your configuration. However, be sure to choose “confold” e.g. use the existing (old) config files for all modules if possible to avoid APT from overwriting your config files with new ones.