Before upgrading, ensure that you have all the required user permissions as mentioned in each database collector configuration.
If you are upgrading the Controller and agents, first upgrade the Controller and then upgrade the Database Agents.
Shut down the Database Agent process before you install the new agent. All Database Agents that are running from the same install location need to be shut down when updating that install location.
Back up the <db_agent_home> directory so you can revert to the previous installation if required. To maintain the same configuration information, you will also need the <db_agent_home>\conf\controller-info.xml file.
If both the old and new agents are >= 4.2, you can keep the old agent running while installing the new agent, allowing you to upgrade the agent with no downtime. Once you see the new agent showing up as "ACTIVE" in the agents page in the Controller, stop the old agent.
Make a copy of the existing agent directory, <db_agent_home>. Backing up allows you to revert to the previous agent installation if you need to. You can also copy over the controller-info.xml configuration file to the new installation to ensure the agent configuration is maintained.
To ensure the agent configuration is maintained, copy the <backup_db_agent_home>\conf\controller-info.xml file to the new installation directory, <db_agent_home>\conf.