Hi,
Are you trying to install the 11.4 agent from scratch or upgrade existing 11.3 agent?
If you are upgrading, then please have a look at this.
If you are just installing a new agent, then download the DVD, copy the setup.bin for AIX to your AIX server and run it.
As for manually removing, you can stop the agent and delete the Agent directory. Then remove the CA Agent service, if you added it to startup (init) using lssrc/rmsys. However, the "Uninstall WA Agent" script in the UninstallData will remove it as well.
Thank you,
Nitin Pande
CA Technologies