As an administrator, you have the ability to delete discussion posts made by members within any group from the Comments Management page.
Deleting a Discussion Post
1. From the dashboard, click Home or the home icon on the left.
2. Click Settings.
3. Find the Community section and click on the Moderate Comments link.
4. Here you should see all of the posted comments. To delete a post, click on the down arrow on the post and click on the Delete option.
5. The post will now be deleted from the group.