Right now the only way to upgrade to Windows 10 is the free upgrade which is available online for eligible PCs. But Microsoft has provided a way for upgrading PCs which are not connected to the Internet. Also by using this method you can save precious bandwidth by using just one media and upgrade multiple PCs. You need to have the Product Key ready for each PC though, otherwise your PC might not get registered.
There is a FAQ available to check or find out where the Windows Key is located.
You need the PC with Windows 10 and it should be connected to the Internet. Next head to the following URL and download the Media Creation Tool from the Microsoft Website.
Remember to choose the correct version for the OS which has been installed.
Once the tool is downloaded, choose Run as Administrator. It opens the following interface.
Choose Create Installation media and click next. On the next screen you will have the option to choose language, version of Windows and the option between 32 bit or 64 bit. Remember, Microsoft has listed out which operating system version can be upgraded to which version of Windows 10. For online upgrade, the choice is automatically picked up. But for the manual upgrade, you need to refer to this table or see the details at this URL.
And next comes the media selection. Good amount of flexibility has been provided by giving us a choice between the USB Memory or ISO file. Make your selection and click next.
The next screen gives you to choose the location if in case it is an ISO file. And then the Media Tool begins its work.
Once the media is ready, use it to upgrade as many PCs as you want.