There are two settings at the page group level that impact deleted items:
When you delete an item on a page, the item is removed from the page unless the page group administrator has selected the Retain Deleted Items option. When this option is selected, items are stored in the database after they are deleted. If this option is not selected, items are immediately and permanently removed from the database when they are deleted.
The Display Deleted Items option allows you to continue to display items on pages even after they have been deleted. Deleted items are visible only in Edit mode, marked with a Deleted flag. If this option is not selected, items are no longer displayed on pages when they are deleted. To display deleted items, you must also retain deleted items in the database.
Both of these options must be selected at the page group level for you to restore a deleted item. Restoring a deleted item "undeletes" the item or restores the item on the page.
Notes:
You must be logged on as a page owner or an authorized user with the appropriate page or item-level privileges to restore a deleted an item.
Only users with at least Manage Item privileges on a deleted item (if item level security is enabled), or at least Manage Content privileges on the page that contains the deleted item can see and interact with deleted items when a page is in Edit mode.
If you restore an item that has sub-items, all the item's sub-items are also restored.
The administrator must perform a system purge to remove retained deleted items from the database.
Navigate to the page that included the item.
Note: If you do not see the page that you want to work with, you may not have the appropriate page access privileges. See your page group administrator to gain access.
Switch to Edit mode.
Locate the item that you want to restore and click 
beside the item.
Click Undelete.
The item is restored on the page.
Deleting an item
Retaining deleted items
Granting access privileges to your page
Granting access privileges to your item