Upgrade to ejabberd 18.01
Ejabberd upgrade process
There is no significant change in code and database since 17.11. There is no specific upgrade procedure. Anyway, due to TLS improvements and ACME support, you need to check your configuration to keep it up-to-date with latest patterns.
While your old ejabberd.yml is still supported, you may prefer to simplify it thanks to latest TLS driver which enables good defaults by itself. You may also need to use the new ACME feature, which requires minor changes in ejabberd configuration file. See ejabberd.yml.example in ejabberd sources for reference.