Update from Windows 8 Pro to Windows 8.1 Pro on a Volume License

Have a production laptop that was originally Window 8.  Since this is a business laptop on a domain, I needed to upgrade to Windows 8 Pro w/ a volume MAK license.  I understand that since it was Windows 8 Pro MAK license, I could not obtain the "free" 8.1 upgrade from the Micro$oft Store App.

With all that being said, I have now downloaded 8.1Pro from my VLSC... a 3+ GB ISO.

Question 1:  Is this a complete OS or the update?
Question 2:  Is this going to reload Windows or will I have an option to only update?
Question 3:  Anyone else pissed off at M$?

I ask these questions because I cannot afford losing data or programs...

Thanks in advance