For a Windows server, follow the instructions in the GroupWise Installation Guide for your version of GroupWise:
GroupWise 2012: Uninstalling the Windows GroupWise Agents
in Installing GroupWise Agents
GroupWise 8: Uninstalling the Windows GroupWise Agents
in Installing GroupWise Agents
GroupWise 7: Uninstalling the Windows GroupWise Agents
in Installing GroupWise Agents