Generally, when upgrading your Mendix application between minor versions (so not Mendix 8 to Mendix 9, for instance) you can simply read the Release Notes for each version to make sure that there are no breaking changes, and so you can see deprecations and other important notes.
Other than what's mentioned in the release notes, upgrading is a matter of:
It is a good habbit to upgrade always to the latest LTS or MTS release. In this case upgrade to 9.12.2