How can I set up Updates [DLC]?

Hello everyone! I was wondering of how I can make updates for my game when its finished for maybe any game breaking bugs are found after I finished it. This is kinda like a few questions combined so I will break it up for you:

When I finish fixing bugs what files do I use for the update?

[Edit] I have tested replacing Data folders with different versions of my game which didn’t work. I’m not sure how I could install the updates without completely removing the whole game and replacing it that way.

How can I check for updates and download them?

What’s the easiest way to set up a script to check for updates and post updates on the Internet. I guessing I can use a public drop box to set up the files but how can I notify the game there is a update? (Please post example or documentation for the script)

Can I have the game download and install the online files?

If it’s possible how do I make a script that can download files, remove current old files and add the new files? (Please post example or documentation for the script)

Also I hope this isn’t a pain to ask (I have seen a few DLC questions here) but I cant find any thing about setting up updates or DLC to standalone games. If there is a site or answered question with the all the information I seek just let me know. Thanks in advance!

http://forum.unity3d.com/threads/131088-Downloadable-content

https://docs.gamedonia.com/tutorials/downloadable-content/unity3d