If you are a member of the group, then you may remove only your own posts to the group archives. Messages can only be removed one at a time. As a group owner or a moderator with proper privileges, you can delete any archived messages in your group.

To delete a message from the archives as a member:

1. Sign in to your Yahoo! Groups account
2. Click Manage next to My Groups.
3. Click the group name for which the message is posted.
4. Click Messages on the left side of the page.
5. From here, you will see a list of all the archived messages. Click on the message that you posted.
6. Click Delete. 
7. You will then be taken to a page to confirm removal. Click OK to complete removal.

To delete a message from the archives as a moderator:

1. Sign in to your Yahoo! Groups account
2. Click Manage next to My Groups.
3. Click the group name for which the message is posted.
4. Click Messages at the left side of the page.
5. From here, you will see a list of all the archived messages. Check the box of the message(s) you wish to delete. To select all of the messages, click Check All.
6. Finally, click Delete.
7. You can also delete your message while it is still open.
8. Click Delete.
9. You will then be taken to a page to confirm removal. Click OK to complete removal.

Your message will then be removed from the group.

Note: Once you delete an archived message, it cannot be restored.