I agree with everything Christer said.
Use the
Media Creation Tool to download Win10. You'll need to use the 32/64-bit version that's consistent with your installed OS, but you'll have the option to download either the 32-bit or 64-bit version of Win10.
When the MCT is launched, the first screen asks if you want to "Upgrade this PC now" or "Create installation media for another PC". I believe that's what may be getting referred to in NightOwl's reply #13, bullet c.
IAC, I would never choose "Upgrade now", I'd always opt for "Create installation media". When you select that option, you'll be offered the choice of downloading 32-bit Win10, 64-bit, or both.
You cannot upgrade a 32-bit 7/8.1 installation directly to 64-bit Win10, but you can do so in two steps: first upgrade to 32-bit Win10, then wipe the partition and do a clean install of the 64-bit version. The first step will have fingerprinted your system to register your digital entitlement to Win10, and then step two will work and be automatically activated.
To each his own, of course, but I prefer creating an iso instead of a bootable flash drive. It just offends my OCD tendencies to have a bunch of single-purpose flash drives laying around that I may never, or rarely, use again in the future.
FWIW, I feel the same way about program and hardware installation floppies, CDs and DVDs; I never keep them. I always create iso images from CDs and DVDs (and bin images from floppies), and store the images in a "Library" folder on an external hard drive. That way, everything is kept in one place and I don't need to fret over keeping track of CD/DVDs and an assortment of flash drives.
In the rare event I need the installation media again, I always have the option of recreating a floppy/CD/DVD on rewritable media--burn, use, erase.
However, program CD/DVDs can be run directly from the iso file if you have a virtual optical drive, without the need to recreate hard media. I've long used a utility called
Virtual CloneDrive on all my XP/7/8.x systems, and the latest version will even work with Win10.
When you install VCD your system's "My Computer" will show an additional optical drive and associate the .iso extension with it. Then, just double-click your iso file and it will "load" in the virtual drive just like a real CD/DVD would load in a real optical drive. If you allow CDs to autorun, it will even autorun. You can install programs from a virtual CD exactly as you would from a hardware CD. The only difference is a virtual CD runs a heck of a lot faster than a real CD.
I could have burned a temporary DVD, but I used the virtual technique last weekend to upgrade two Win7 computers to Win10 (just to have them fingerprinted, before reverting back to images of Win7).
- I installed Virtual CloneDrive in Win7;
- copied the Win10 iso file to the system's data partition;
- double-clicked the iso to load it into the virtual DVD drive;
- launched setup.exe from the virtual DVD and clicked through the first couple screens;
- left and came back when Win10 had finished installing.
edit: re reply #13 bullet d...
No, I have seen no evidence Win10 modifies the system BIOS. You can't "patch" a BIOS, you have to reflash the whole thing, and given the wide variety and proprietary nature of OEM BIOSes, that would seem an insurmountable barrier.