Now that Ops Center 12.2.1 is out, I thought I'd give a brief walkthrough of the upgrade process.
The first thing to do if you're planning on upgrading to 12.2.1 is checking the upgrade paths. If you're using an older version of Ops Center, such as 12.1.4, you'll have to upgrade to version 12.2 first. Here's a flowchart that shows the supported upgrade paths:
Once you've figured out your upgrade path, you should check the release notes. They have a list of known issues that could be relevant to your environment. In particular, if you're using version 12.2, there's a patch that you have to apply if you want to upgrade through the UI.
Once you've taken a look at the release notes, the Upgrade Guide will take you through the upgrade itself, with different procedures based on how you're doing your upgrade (through the UI or command line) and what sort of environment you have.