In addition to managing user access via Roles, you can assign Groups to Users to control which Forms / Devices they have access to. (Check out this help article for more information on how to create these Groups.)
Managing the User Groups is done from the same edit page as the Users Role.
First, after logging in to your account, navigate to your dashboard. On the left side of the page you'll see a "Settings" button. Click that button and then click the "Manage Users and Roles" link that appears underneath. You'll then be brought to a separate page.
To alter the user, click the Edit button on the right hand side.
Then, navigate to the "Groups" section and tick/un-tick the groups.
Click "Update User" and you're done!
If you have any questions or comments feel free to send us a message at firstname.lastname@example.org.