I am currently running 4.0.3 SOURCE version with several child portals. All is working fine.  I want to upgrade to the just released 4.3.0 version.

Question: 
 I see there is a DotNetNuke 4.3.0 UPGRADE.zip file. Do I use this zip file to upgrade FROM 4.0.3 TO---> 4.3.0? (remember I am currently using 4.0.3 SOURCE version.

Do I just unzip the DotNetNuke 4.3.0 UPGRADE.zip over  the top of my 4.0.3 setup?
Do I use the DotNetNuke 4.3.0 SOURCE.zip and unzip this over the top of my 4.0.3?

Whats the Difference between the UPGRADE and the SOURCE?

(Yes, I will backup my web.config and save the machine keys)

I know this seems simple, but I just dont want to mess up. I have never used an "...Upgrade.zip" to do a DNN version upgrade. I always just used the next version of SOURCE and unzipped it over the current install and all worked fine.

Thanks in advance.

David