You should be able to download and burn a windows 7 cd of the variant you need, 32 bit or 64 bit.
They are all have the full code, your specs are unlocked by your activation code.
Get it from a reputable site like Microsoft so it will not come with malware installed.
It is a good idea to have a bootable dvd around since it can do some repair work.
ya, did not suggest that download usb thing due to all the issues that can surrounding it , but may work fine ?? all you can do is try and see where you end up with it .
I'm a firm believer to all ways have a retail / oem dvd copy - for as said above and never recommend ''upgrading a os like from 7 to ??? cause then if something goes wrong you maybe 100% out of your old and upgrade and buying another copy of windows disk anyway ..