Last tested: Jul 10, 2018
If a user or a group of users aren't seeing the Edit button in the top right of a User UDD, then most likely the user/group only has View folder access. Meaning they can view content in this Space, but cannot Manage Access, Edit. See this doc for more descriptions on the folder Access permissions and how to add / edit the permissions.
Chat Tip: This can occur both in the standard use case (users with Looker accounts) and in SSO Embed. For SSO Embed, the SSO user and/or SSO group that is generated in the script will need to be added to the folder permission as needed.