The Trash settings allow you to set the duration that items will remain in the trash of your managed users accounts. After the time period the items will be permanently deleted. These settings can be found in the 'Content & Sharing' tab of the "Admin Settings"
Please note, items contained in the trash still count against your total storage allocation, so choosing "Keep all deleted items" may impact your ability to upload new content.
To save your changes click the 'Save' button