Deleting messages in WhatsApp

I had a lot of private and group conversations over a year through WhatsApp, but all of a sudden the space it takes seems to be on a high. I was able to delete private messages by long-pressing the person’s file and deleting the entire conversation, but when I long-press the group chats, I didn’t quite find an option to delete the conversation all at once.

Is there any way to delete private messages all at once rather than doing them individually?