Click on the group profile image as directed by the arrow, as shown in the figure below.
Go to Settings, as shown in the figure below.
A Settings window opens.
View at the DELETE section.
Note: Delete All Messages and Files was the default option selected.
Click Submit as directed by the arrow, as shown from the figure below.
Confirm your selection as directed by the arrow, as shown in the figure below.
All messages and files of this group are deleted successfully.