When you install Attachments Cleanup Assistant you will unlock new feature in Confluence content actions called “Check Attachments”. It will be available on published pages.
Feature will be available on:
published pages
with respect to permission as it operates as User
When you click “Check Attachments” action a popup will open.
For a brief time it will scan the content of the page to cross check displayed attachments and attachments added to page.
Currently app only check for displayed attachments on page, it doesn’t know if it is used/referenced somehow on any other page
Then it will show results:
From this place you can:
close the window with “X” or by clicking away
use the “?” button to go to documentation in new window
click on file name to preview image in new window (and move to page attachments)
click on “Delete” button, to remove unused attachment
Delete will not ask for confirmation, that is the purpose of the app there is no need to slow this down 
If you decide to ‘Delete’ attachment, the content of the modal window will refresh
It doesn’t refresh the page, so if you are using attachments macro to display the attachments you need to refresh the page.
Is it gone?
Attachments Cleanup Assistant removes attachments from pages, but … Space Administrator can still restore that attachment (if needed) or purge them!
Note to Space Administrators:
Remember to purge attachments from time to time, but give enough time for users to notice any missing attachments