Trash

When you delete a file you should see a pop-up that explains the files are moved to the Deleted Files folder for 30 days and it gives a link to that folder:

https://assets.adobe.com/deleted

Go the link in your web browser and you will be able to delete the files you no longer need. To delete multiple files, click the thumbnail whilst holding down the Shift key.

You can do a whole row, or a page, by clicking the first and last image and it will select everything inbetween if you keep the Shift key held down.