You can see the history of sending and receiving files in the 'History' menu
You can also tap All ▼ at the top to split the list into 'Sent' and 'Received'.
Tap Edit in the top right corner to switch to edit mode. Select the items you want to delete or tap Select All at the top to delete them.
Select an item to see a list of files. Tap a file item in the list to launch it or zoom in on it.