I should have posted this earlier.
To upgrade your Windows phone to Windows 10 Mobile, you will need to install and run Upgrade Advisor which can be downloaded from Microsoft Store on your Windows phone. This is the only way to upgrade. Many Windows phone users have been waiting for their phone company to push this upgrade to their phone, this won’t happen.
I was about to give up my Windows phone running Windows 8.1 Mobile and get a Google Pixel, until I upgraded my Windows phone to Windows 10 Mobile last year. It is so much better!