Click on the people tab on the left side of the screen. Then, select the person you wish to remove by clicking on his/her name.
From there you will see a quick overview of their information. You will be able to remove them from whatever group you would like by clicking the remove option that is to the right of that particular group.
You can also remove them from a group within the groups tab. If you go into the group that you are wanting to remove people from, you can do so from the members tab of that group.
On the right side of people’s names, you can click the trash can icon to remove them from that group.