When I first received my S4, I determined I would not use most of the pre-installed "junk-ware" apps that Samsung/Verizon preloaded on the S4 (they cannot be uninstalled unless the device is rooted, & I didn't want to root my S4). So, I disabled them to prevent them from eating up CPU cycles, slowing my S4 needlessly, should they be setup to run in the background on my S4.
Prior to performing the update, I re-enabled those "junk ware" apps.
This may have been unnecessary, but I did this as a precaution because the scant update information identified at least 2 of these "junk ware" apps would be touched by the OS update.
I downloaded the update using the S4's Wi-Fi on my high speed Internet connection.
To ensure I had a strong Wi-Fi signal, and no dropouts during the download, I did the download in the same room where my wireless router is located. It turns out that the update download is verified after the download completes, so had I experienced a Wi-Fi drop out, the verification would likely fail and allow a download retry.
The update download completed in about 10 minutes.
The update install took about 15 - 20 minutes, followed by an automatic restart with a message that said the update was successful. Not bad, the entire update process took less than 30 minutes.
I performed a couple of restarts, just for good luck.
The entire process went smoothly and my data (contacts, memos, etc) & downloaded apps remained intact and undisturbed.
Now, 3 of my 4 downloaded apps show the option to be transferred to my SD card. In time, I'm hoping all the apps developers will do their future updates such that they allow installs/transfers to the SD card.
Using Chrome, I tested my Internet access and that worked just fine after the update. My S4 Internet connectivity remains stable very fast, and continuous, no issues. Also, battery drain appears normal & unaffected after the update.
I'm seeing posts, here, saying that doing the update using the "Software Upgrade Assistant (Samsung)" that needs to be installed on a PC or Mac is very slow. That may be due to a slow/poor Internet connection, or something related to an issue with the Samsung update servers. So, I'm glad I chose the "over-the-air" update approach using Wi-Fi.