Please be aware when you Archive an Item, the Item is not lost forever. Instead, the Item no longer appears as live but can be found in Reports under Archived Items. You can restore any Archived Items by navigating to Archived Items and selecting 'Restore'. Read more about this here.
To bulk delete/archive items:
Go to the reports tab
Select all of the assets you want included in the bulk archive
Select ‘Bulk Edit’
Select ‘Bulk Archive’
Select ‘Confirm’
For further information, a short tutorial on bulk editing assets can be viewed below.