Transferring files / Replacing old site

Hi guys, I use Dreamweaver CC, and would like to know the best protocol for when completely replacing all the files of an existing website (including new CSS, etc) with a set of brand new files (ie. a brand new site) - but most importantly, without losing any of the new CSS formatting during the process of moving them from the Test folder to the main local site view, ready to upload. 

My new site is currently residing in a Test folder on the old existing site, so needless to say I need to replace the existing local files with the new files, before uploading them to the remote site.   But in the past I have tried various methods of doing this - and sometimes have lost all my CSS formatting during the process (such as by opening the Windows 'folder' view of the Test files (ie. outside of Dreamweaver) and copying the files to the folder where the main local site is located.   The only foolproof method I have found (for my main content files - but which takes forever!) is opening each new file individually, and then Saving it to the local site folder (via File / Save / Save As) - but needless to say, that can take an eternity.  I am sure there must be a method that takes two seconds flat - so thought I would come to the experts and see how you do it.   Appreciate your thoughts and time.

Cheers,

Craig