OneAgent has a dedicated uninstall program. You'll need to run it to remove OneAgent from your system.
Go to the /opt/dynatrace/oneagent/agent directory and, using root rights, run the uninstall.sh script.
Following uninstallation, log files, the user running OneAgent, and part of the configuration are preserved in the OneAgent installation directory. These can be removed manually. Note however that if the configuration files have been removed, and OneAgent is re-installed, the host will show up as a new host with a different internal identifier.
For a complete OneAgent uninstallation, remove the following:
/var/log/dynatrace/oneagent/opt/dynatrace/oneagent/log/var/lib/dynatrace/oneagent/agent/config.dtuser.