All you need: https://www.microsoft.com/software-download/windows10
It's free for you.
I have a Dell Inspiron One All-in-One computer which is over 5 years old, but still in very good condition. It was on Windows 7 64 bit Home Edition. After loading free upgrade to Windows 10, the computer does not start readily. I have to reboot with ctrl-alt-del several times. The message I get is that boot information is missing. Several times, I have gone to BIOS and selected default settings, during re-boot. That has not resolved the problem. Dell no longer provides support to this model of computer. However, Dell informed me that I must re-load the OS with the help of third parties. My question is, should this re-loading of OS be done only from a media? Will Microsoft allow me to download Windows 10 once again? Would that really solve the problem? Or should I format the HD and re-load the OS afresh? Do I have to buy the OS? I would be grateful for any input from the learned members of this forum.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic