The following commands will allow you to remove/uninstall Altiris Client, known as AClient, without knowing the Altiris password. However, you still must be logged in as an administrator on the computer before doing this procedure.

Open Command Prompt

Uninstall: c:\Program Files\Altiris\aclient\aclient.exe /remove /silent
Remove directory: rd /s /q "c:Program Files\Altiris"

I recommend using CCleaner to remove the now unsed registry keys that were associated with Altiris.