For the most part, the Windows 10 upgrade from Windows 8.1 seems more like a patch than an entire version upgrade. Everything seemed to work the same as it always had. Yeah, I know there are some significant changes, but it’s not as if you feel it’s totally new…like the jarring change from Win 7 to Win 8.1. That said, if you are an Windows 8.1 user and have a highly customized your Start screen, I have a warning for you: After you upgrade to Windows 10, your Start screen will be totally hosed.
Basically, Microsoft shoehorned the 8.1 Start screen into a scrolling box. It probably would be ok if the upgrade just put your old 8.1 Start screen into it, but noooooooo, you end up with a very truncated version. Kinda stupid since there is an option to make it full-screen similar to 8.1.
My recommendation is to take some screenshots of your 8.1 Start screen before you upgrade. Then, you’ll have something to use to rebuild your Start screen after the upgrade.
Make Start full screen
To make Start screen full screen and see everything in one view, click the Start button, then go to Settings > Personalization > Start, and turn on Use Start full screen.