1. Click on the "Files" tab at the top of your workspace.
   
   
   

    

2. Find the file you want to find the file history for and set your mouse over the filename to reveal additional information for the file.  Click on the number of revisions the file has, pictured below:

   
   
   
   

3. You'll be presented with a list of revisions.  These dates and times represent every time the file (with this exact file name) has been uploaded.  This listing is ordered by date, so the current version is always the top version.  Click the "More" button for the version of the file you are interested in.  Click "Download" to download that revision, or "Revert" to revert the file. 
   
   

   File revision list

   
   

    

Tip:  You can also get to the File History of any page by clicking the History link in the File Options menu of the file page, shown below.