There are 2 ways to remove an auto-share user.
The first way is to navigate to any of the users posts and hover over their thumbnail. An "Auto-Share" button will appear where you may select to activate or disable auto-sharing.
The second way it to navigate to the tribes page and remove the user on auto-share.
Go to the "Tribes" page. On the right hand side is a heading titled, "Auto-Sharing".
Click on "Show all" to display all the people you are auto-sharing.
If you are in an Atomic or Automatic tribe, you will need to leave the tribe to disable auto-sharing.
If you are a Prime or Prime Lite member, you may auto-share content from individuals, in which case all you need to do is click the "Switch to Manual" button to disable auto-sharing.