OK, I'm going to answer my own question here... I have to admit I was a bit insulted by the upgrade screencast; I don't need to watch a 7-minute video of some dude using FileZilla.
Here is how I did my 1.40 to 1.50 upgrade (the No Source version with no code customization aside from the theme)
1) Backed up my existing site files.
2) Backed up my existing site database.
3) Download nopCommerce (with no source code): nopCommerce_1.50_NoSource.rar and extract it to its own folder
3) On the current site database, run this script from the new version: \nopCommerce_1.50_NoSource\Install\Scripts\1.50\nopCommerce_upgrade.sql
4) Use
WinMerge to merge changes from old files to new - EXCLUDING ConnectionStrings.config which has my specific server info
5) Since I added a new theme, I had to tweak the CSS for that - at this point it was kind of trial & error. I did a diff between the new version of the nopClassic theme and my custom theme (in the App_Themes directory), that helped. One important thing to know is that the new themes add a new stylesheet file called "styles.css" that seems to replace some of the stuff in the other style sheet files.
Hope this helps someone out there.