Adding administrative users to the agsadmin group
Before you attempt to connect to your GIS server, you need to grant yourself administrative access to it. You do this by adding your operating system account to the agsadmin group, which contains a list of users who can administer the GIS server. If there are others in your organization that need to administer the GIS server, you can add their accounts as well.
Don't worry if you don't have the complete list of administrators; you can always add and remove accounts later. It's important to note that the accounts you add to this group will be able to add, delete, and modify services running on the GIS server.
If you've added an account to the agsadmin group, you do not need to add it to the agsusers group.
Right-click the ArcGIS Server administrators group, agsadmin, and click Properties.
The users of the accounts you add to the ArcGIS Server administrators group may need to log off and back on before the new settings take effect.