system
A chat on subreddit /r/pcmasterrace
human
Download the Windows 10 / 11 ISO from Microsoft. Burn it to a flash drive, reboot your PC and boot off that flash drive. Follow the installation prompts and choose to format the drive you're installing Windows to.

Your Windows license is either tied to your Microsoft account, or is embedded in the system you bought and is digital. Either way it's a really good idea to tie your Windows licenses to a Microsoft account so you don't have to fuck with calling them if you change hardware.
gpt
Of note… if you visit the site from a Windows computer, it’ll prompt you to download the “media creation tool” instead of the .iso file. 

I don’t know if the media creation tool will also create the new tumbdrive with all the OEM bloat or not. 

But if you want to .iso file, you’ll have to change your user agent to Mac or linux.