Let’s clear the air. “Free Windows 10 upgrades for one year” has lead many to think that this means you will have to pay a yearly fee for the OS, much like Office 365. Not so.
If you are running an up to date copy of Windows 7, Windows 8.1, or Windows Phone 8.1, you will have one year, from the launch date of Windows 10, to grab your free upgrade. Once a year has passed, you will be required to pay for your upgrade on the PC and tablet side. On the phone side, the OS will remain free, as it’s usually up to the OEMs and carriers to issue OS upgrades to their phones. And, of course, I’d like to point out that no one has ever charged an end user for an update on a phone, so I doubt we’ll be seeing Microsoft start down that untraveled road.
Will you be required to use your upgrade product key right away? Probably not. You may have to download some small tool to the PC or tablet to verify the device is eligible for its free upgrade before spitting out a product key and asking whether you’d like to update right away or later. I assume these keys will be good indefinitely, or for one year after you are issued them. You will always be able to grab the ISO or an installer and save it for later usage.
You should also be able to use the product key to jump from an x86 installation to a 64 bit one, but you’ll have to do a clean install of course, and keep in mind that some tablets may not have x64 drivers available before you make that choice.
We will find out more as the RTM draws closer, but I don’t expect the process to differ much from Windows 8.1. There may not even be a “Pro” SKU, just Windows 10 and Windows 10 Enterprise alongside Windows 10 Holographic and the version for devices under 8 inches, which would be phones and very small tablets.