By default, any group participants can send messages and change group information including, the group subject, icon, or description. However, a group admin can change group settings to allow only admins to edit group info or send messages.
Change the settings for editing group info
Open the WhatsApp group chat, then tap the group subject.
Alternatively, tap and hold the group in the CHATS tab. Then tap More options > Group info.
Tap Group settings > Edit group info.
Choose to allow All participants or Only admins to edit the group info.
Tap OK.
Change the settings for sending messages
Open the WhatsApp group chat, then tap the group subject.
Alternatively, tap and hold the group in the CHATS tab. Then tap More options > Group info.
Tap Group settings > Send messages.
Choose to allow All participants or Only admins to send messages.
Tap OK.
Note: Participants can directly contact an admin by tapping admins in the group, then tapping the name of the admin they'd like to message.