Only a Group Admin has the option to remove another group member. To do this the Group Admin has to follow the below steps:
  1. Go the the group
  2. Tap on the three dots from upper right corner
  3. Tap manage members
  4. Tap on the three dots next to the group member that they want to remove
  5. Tap Remove from group
  6. Confirm the removal
By removing a member from a Public group, it will make them not be able to post, comment or see the content of that group anymore, but if they know the name of the group they can alway rejoin the group.
By removing a member from a Private group, it will make them not be able to post, comment or see the content of that group anymore and they won’t be able to join the group in future without an invite.