Removing via the segment itself
The first thing you need to do is to navigate to your segments list in the main Mautic navigation menu.
Currently this can be found as the 5th menu item on the navigation panel which is displayed on the left of your Mautic instance, as highlighted on the image in red.
Clicking on Segments will display a list of all the segments you have set up in your Mautic instance.
From this point, you can identify the segment which you wish to remove the contact from either visually by scrolling down the list, or by using the search bar at the top. Once you have identified the segment, on the far right there will be a blue 'lozenge' which shows the number of contacts who are in that segment.
If you need to remove somebody from a segment, click on this for the relevant segment, which will show a filtered list of contacts who are in this segment. Now you can find the user you need to removem either by scrolling or by using the search facility at the top of the page.
On the first column in the row representing the user you wish to remove, there will be a small downward facing arrow - click this, and select 'remove from segment' to remove that user from the current segment.
Removing via individual contact preferences
Thanks fo @yourdigitalclub on Mautic Slack for highlighting that you can also accomplish this for an individual contact by navigating to the 'preferences' menu item here:
Once the contact preferences popup is open you can amend segments using the 'Segments' tab:
Removing via contacts list and bulk-removing from segments
If you have multiple users to amend, or you just want a quicker way to manage contact segments, you can do this via the contact list.
Simply navigate to Contacts (third on the main Mautic menu) and select the contact/s you wish to remove from a segment. As soon as you check the box, the down-facing arrow at the very top will turn green, and indicates there are options available to you. These include changing the campaigns, segments and stages for the selected contacts.
This is a pretty powerful way of managing these in bulk - but with great power comes great responsibility, especially if you are kicking off a campaign based on these factors! Check and double check before making any bulk changes!
Note: This was captured using Mautic 2.7.1 - it is possible there may be future changes in the user interface that alter the process!