In the middle of the left panel, you have a section which serves to manage users with access to this board.
1. Click on Users section button.
2. You will see now all users added to this Board. They will be grouped by their permission level: Owners, Members and Visitors.
When you are an owner of this board, you can add users from here using the +Add button in every group.
3. Click on
and then on Manage users button to add or remove users or user groups.
You can also see here permission levels of users to this Board - who is an Owner, Member or a Visitor.
To remove the user, hover over his name, select more button and then select Remove from group.