Each group chat has an owner (the person who created a group chat) and participants.
The owner can:
Delete the chat
Edit the chat in the following ways:
Add new participants
Delete participants from the group chat
Change the name of the chat
Change the photo of the chat
Participants of a group chat can:
Leave the chat
Edit the chat in the following ways:
Change the name of the chat
Change the photo of the chat
It is not possible to edit or delete messages which have been sent.