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 or archive items:
Go to the Reports tab.
Select all the assets you want to include in the bulk action.
Click Bulk Actions.
Select Archive and confirm the action.
For further information, a short tutorial on bulk editing assets can be viewed below.