You will need to manually delete notices after they are not needed or set automatic expiry by using the post expirator.
Delete Single Notices
Find the Notices menu on the left-hand side navigation menu. Click 'All Notices'.
Mouse-over the Notices you wish to remove and click Trash.
If you accidentally remove the wrong Notice you can restore it from the trash bin.
Note: Items are stored in the Trash for 30 days before it is permanently removed.
Delete Multiple Notices
Again, go to the Notices menu in the Dashboard Navigation menu and select All Cards
Select the checkbox at the top of the list to select all, or check each item individually
From the Bulk Actions drop-down, select Move to Trash option
Click the Apply button
Recover Trashed Items
You can recover notices you have moved to the trash, and not deleted permanently.
Open Notices > All Notices
Click on the Trash link at the top of the list.
Hover over the notice you want to restore, and click the Restore link.