Outdated Windows 10 installation files and upgrade issues

Hello guys, I have a problem and some questions for you. Thank you for helping out, your support is very much appreciated.
Here is my case. In August Windows 10 downloaded itself on my system, but without my consent, since I had not reserved it. It then tried to install, but failed. I noticed this anomalous behaviour through Windows Update, where several instances of these failed attempts were recorded. I then decided to disable automatic updates, in order to obtain Windows 10 later at another time, since I was not ready for it yet. And I proceeded to install regular Windows 8.1 updates.
Now, some months later, I feel like the time for trying out Windows 10 has come, but I'm afraid Windows 10 installation files stored months ago in the C:\$Windows.~BT folder may be heavily outdated and thus cause issues. Moreover, in the meantime, people at Microsoft announced the specific problem which was previously determining failures in my upgrade process had finally been addressed and solved over later (more recent) Windows 10 installations.
Now, what should I do to obtain an updated Windows 10 installation package? Will automatic updates, once they're turned on and I have reserved my Windows 10 copy through the apposite tool, just do everything required? Will the old installation files at C:\$Windows.~BT be recognized as outdated and consequently overwritten?
In case I were to use the Media Creation Tool as a last resort in order to upgrade, should I remove the $Windows.~BT folder and all of its content beforehand?
Thank you for your time, answers and precious help, because I do not really know what to do

Just download Media Creation Tool.
Image your drive with Macrium Reflect Free before doing anything.
Find your Windows 8.1 key!
If your using Firefox and Thunderbird you can use MozBackup. Also try Ninite to install lots of apps.
At this point you can do an upgrade or do a clean install. Then you can copy your data over. And re-install your apps.
Good luck

Slugger said:

Just download Media Creation Tool.
Image your drive with Macrium Reflect Free before doing anything.
Find your Windows 8.1 key!
If your using Firefox and Thunderbird you can use MozBackup. Also try Ninite to install lots of apps.
At this point you can do an upgrade or do a clean install. Then you can copy your data over. And re-install your apps.
Good luck

Thank you. Is Firefox not working after the upgrade, is that why I should use Mozbackup? Also, I noticed a 7,3 Mb .exe file is offered by clicking "upgrade now" button at Windows 10 Will this do the trick too?
One more thing. Windows came pre-installed on my laptop. I used Nirsoft Product Key to find my Windows 8.1 key. Is that a good, reliable solution?

Ztruker said:

Use ShowkeyPlus for your key, though you shouldn't need it as the Windows 10 installer will read the embedded key from BIOS for activation.

Download the Windows 10 MediaCreationTool to upgrade with or create a flash drive or ISO that you can burn a DVD with. Forget Upgrade now. Scroll down and click on the Download tool now button then run it.

Excellent tutorials here for upgrade or clean install.

Windows 10 - Clean Install
Windows 10 - Upgrade Installation

Thank you for your useful advise