You need to be the owner of the group to be able to do this.
How to add a member
- Click the People icon

- Click on Manage groups

- Select the group you want to add members to
- Click the three dots, then on Add members

- Search for the people you want to add and click on Add
- They will then show in Group members
How to remove a member
Follow steps 1-3 above
- Click on Members
- Click on the X


You can also change current members to Owners if you would like to delegate this to someone else.