Just like you can edit the name of a group, you can also edit the members of the text group. As long as there are more than four members in the group text and each user has an Apple device, members can be added or removed from the group after its creation.  To remove a member, select the group text you wish to edit and tap the group icon at the top of the thread. Next, look for a gray arrow icon on the right of the contacts and select it.  Swipe left on the name of the contact you want to delete from the group. Click "remove" and then "done" to remove the group member from the group.