ActiveGate has a dedicated uninstall program. You'll need to run it to remove ActiveGate from your system.
On Windows:
Go to Control Panel > Programs and Features and uninstall Dynatrace ActiveGate.
On Linux:
Go to the /opt/dynatrace/gateway directory and, using root rights, run the uninstall.sh script.
Following uninstallation, log files and part of the configuration are preserved in the ActiveGate log and configuration directories respectively. You'll have to remove these files manually.