This is described in the release notes (I think 2 pages up from the instructions you've pasted):
From version 7.3.2 or any other 7.3.x version:
• Activate the repository for the new version. See Activate the repository
• Upgrade to the new version. See Upgrade from 7.3.2 or other 7.3.x
Activate the repository
Activate the repository for the new version before upgrading from version 7.3.2 or any other 7.3.x
1 Log on to the appliance you want to upgrade on a system console, using SSH.
2 Run the following command:
You can now upgrade to the new version.