I have a file A in Desktop 1 that will upload to Server 2. I also have a copy of file A in Desltop 2. I want to make sure that file A in Desktop 1 will be automatically synced to file A in Desktop 2. How?
You don't. To ensure Device A and Device B contain the same working files, GET (download) working files from your remote server.
If you work in a collaborative setting with multiple users, look at Dreamweaver's file check in/check out feature. This ensures that people can't access and overwrite files that you are working on and vice versa.
In addition to what Nancy said, you can also setup a git repository to help manage version control across multiple computers/users who are trying to work on a site. https://helpx.adobe.com/dreamweaver/using/git-support.html
The solution that Nancy offers is the solution provided by Adobe. It is the only 'practical' solution you have on hand out of the box.
The GIT solution, that Ben introduce, is also a great solution, but often overloaded for an everyday ediatble web site
For my part, I have been working for years with collaborators who use Dreamweaver on a daily basis. And, we tested many solutions outthere, So to make sure that our desktops are always in sync, we have used mapped disks for long... https://www.lifewire.com/net-use-command-2618096
so that way our local disks are actually the same one as a shared disks accessible by network.
If either of us modify a file, it is in fact the same file.
CAUTION... The only real problem is that, contrary to the solution proposed by Nancy, with this method nothing indicates to the users that the file is already being used by another user.
so why do it this way... well actually the use of checking-in and out... is quite complicated (long process), and quite often full of errors... well not when used in a week... but after 6 months of intensive use... it becomes erratic.