Its been a while since this post but since i could not find anything else about this on the internet i decided to post an answer anyway.
(First on a copy of the server to test, always test before updating live.)
1: docker-compose down
2: open .env file with nano and change the v1.0 to the number you want (i decided to upgrade to each version in between just to make sure it didnt skip any update processes, so just repeat these steps each time)
4: docker-compose up -d
5: docker exec -t scalelite-api bundle exec rake db:migrate (this was only needed for v1.1 and v1.2 according to the release notes, obviously if you decide to update from 1.0 to 1.3 or higher you will have to also execute this command i guess, but as said previously, i upgraded to each version in between, so only executed this on 1.0->1.1 and 1.1->1.2)
This should leave you with an updated scalelite (i did have to reboot my server on one update because the scalelite didnt seem to be reachable but was immediatly back online after a reboot, ymmv)
This worked in my case without any issues, dont shoot the messenger if you have problems.