Here's the manual procedure to clear the Dropbox's cache folder.
Clearing the cache can be quite useful when you want to permanently delete files from Dropbox!
When you delete a file or folder from Dropbox, a copy of the latter will be kept in a hidden folder for a duration of 3 days.
To permanently delete these files it is recommended that you clear the cache.
The steps are described below:
The first step is to open the Dropbox folder (C:\Users\Username\Dropbox).
To access the cache, click in the address bar of Windows Explorer and add the following path to the existing address: \.dropbox.cache