Get the Pro Pack from Microsoft to upgrade from 9.1 Home to 8.1 Pro. No real installation required, the pro pack just unlocks some features and leaves you with Pro. This is what I did when I got my Lenovo K450 desktop last year.
See here: Add features - Microsoft WindowsAdd features to Windows 8.1 *
If your PC is running Windows 8.1, you can get Windows 8.1 Pro Pack and enjoy all the features of Windows 8.1 Pro as well as Windows Media Center for $99.99 USD ERP. To buy Windows 8.1 Pro Pack, follow the instructions on this page.
You'll lose Media Center when you upgrade to Windows 10 but that's most a who cares.
"Never Say Never" on a clean install until you have run it for a bit! Things may seem to be going well at first until something goobers on you! You won't be smiling then when finding out that a clean install will then become a necessary.. Plus we are presently running the 10240 build released on the 29th while tthe 10525 build just made an appearance suggesting MS is using the free upgrade at the moment a large beta test without us knowing about it! It's too much like 7 saw the RC which ran very well but still wasn't the final finished product!
I see 10240 as the actual release and 10525 as a beta from which things will be cherry picked to be eventually sent to 10240 users in the form of updates. Any subsequent builds sent to insiders will be treated the same way. We will most likely not ever see an entire new build unless this mysterious SR1 update actually happens and changes the build number. The upgrade is in no way a beta test and the build number may not ever even change. The users of 10240 are the install base. The insiders receiving the test builds are the guinea pigs and are a small minority of Windows 10 users.
For me Media Creation tool was the Best option. I was not able to Download Updates in Windows 8.1 to see the Windows 10 Upgrade notification. But Thankfully the Tool helped me to Upgrade to windows 10 without much hassle.
On upgrading a 7 laptop the Start button wasn't even seen on the initial upgrade install. The Settings screen was nothing but a blank screen. And when going to right click on anything all you saw was a thin verical line for the right click menu. Something didn't go on fully this time using a dvd burned with the Media Creation tool. The second was a full clean install that saw immediate results however and is now being replaced from the 32bit upgrade over 7 HP x86 to the 64bit 10 Home following the first clean to verify the upgrade had been activated since you couldn't see anything in System!
I can't copy that link into this thread because it is a link on YOUR computer. If you follow Brink's tutorial steps, doing it on your computer: Click lower left start button, click Settings, click Update & Security, click Activation, there should be a box on lower right that says "Go to Store", click that.
Brink's tutorial itself is at: Upgrade Windows 10 Home to Windows 10 Pro - See Step 2 in particular.
The only cheaper alternatives I can find are on Amazon.com with $80-$95 Pro Packs or Upgrades for Windows 8 to Windows 8 Pro. I won't even talk about eBay.
If you're at Win 10 Home now and it's activated OK, the Go to Store box should be there for you and, if it's worth $100 to you to go to Pro, then that's about as "official" a path as I see at the moment.
I was looking for a standalone offering in the MS Store. No wonder I couldn't find it.
I didn't notice that tutorial existed. I'll look for the button when I'm next on the Win 10 Home laptop. (No chance that I'll actually use it. I don't really need Pro on my desktop PCs, but I upgraded from 8 .1 Pro.)