Add users to the agsusers group on Windows
On the SOM machine, start the Computer Management application. Computer Management can be found in the Control Panel under Administrative Tools.
Expand System Tools, then Local Users and Groups, then Groups.
Right-click the ArcGIS Server users group, named agsusers, and click Properties.
On the Property page, click Add and, in the dialog box that appears, add those operating system accounts to which you want to grant access to the GIS server. These are typically the accounts that people use to log in to the network from their own computer. Note: You don't need to add administrative users to this group. Administrative users already have user-level privileges to the services.

Window 7 (64 bit) Control Panel >All Control Panel Items >Administrative Tools > Computer Management > Local Users and Groups - Administrators