Sourced from the Microsoft support documents:
1) No restart/reboot after running the update command
2) Microsoft's posted command uses yum update, not yum upgrade.
"In order to upgrade the mssql-server package, execute the following command:
sudo yum update mssql-server
These commands will download the newest package and replace the binaries located under /opt/mssql/. The user generated databases and system databases will not be affected by this operation."