Operating system help needed

[SkulleonYT]

So I just recently built my new gaming computer, and so I found what I though was a product key on a website but it turned out to be like a developer preview or something, it was windows 8.1 pro build 9600, and always had a watermark in the bottom right saying "Activate Windows go to PC settings" and i tried it but I needed a valid product key. (Yes I used the windows media creation tool on my USB to get 8.1 pro) and so my neighbor got me a USB with a copy of windows 10 that I wouldn't need a product key (legal not a crack, dont worry) so I then proceeded to remove all of the files off my PC using the computer settings but was surprised when it was finished that it was back to the windows 8.1 setup screen. So I need to know how to completely remove EVERYTHING off of my hard drive, including the operating system so I can install Windows 10 now. Help much appreciated.... Thanks all!
PS. If you need to know I have a Seagate 1 tb hard disk drive

 

[USAFRet]

So I just recently built my new gaming computer, and so I found what I though was a product key on a website but it turned out to be like a developer preview or something, it was windows 8.1 pro build 9600, and always had a watermark in the bottom right saying "Activate Windows go to PC settings" and i tried it but I needed a valid product key. (Yes I used the windows media creation tool on my USB to get 8.1 pro) and so my neighbor got me a USB with a copy of windows 10 that I wouldn't need a product key (legal not a crack, dont worry) so I then proceeded to remove all of the files off my PC using the computer settings but was surprised when it was finished that it was back to the windows 8.1 setup screen. So I need to know how to completely remove EVERYTHING off of my hard drive, including the operating system so I can install Windows 10 now. Help much appreciated.... Thanks all!
PS. If you need to know I have a Seagate 1 tb hard disk drive

During the OS install, when it asks 'where', select Custom.
You'll see several partitions.
Select each one, and delete. Leaving one large space.
Let Windows install to that, creating what it needs

 

[SkulleonYT]

So I just recently built my new gaming computer, and so I found what I though was a product key on a website but it turned out to be like a developer preview or something, it was windows 8.1 pro build 9600, and always had a watermark in the bottom right saying "Activate Windows go to PC settings" and i tried it but I needed a valid product key. (Yes I used the windows media creation tool on my USB to get 8.1 pro) and so my neighbor got me a USB with a copy of windows 10 that I wouldn't need a product key (legal not a crack, dont worry) so I then proceeded to remove all of the files off my PC using the computer settings but was surprised when it was finished that it was back to the windows 8.1 setup screen. So I need to know how to completely remove EVERYTHING off of my hard drive, including the operating system so I can install Windows 10 now. Help much appreciated.... Thanks all!
PS. If you need to know I have a Seagate 1 tb hard disk drive

During the OS install, when it asks 'where', select Custom.
You'll see several partitions.
Select each one, and delete. Leaving one large space.
Let Windows install to that, creating what it needs

Do you mean while setting up the windows 10 usb? i cant get my computer to boot using that usb to start installing windows 10, instead it just boots to windows 8.1 that i already had installed, it takes me to where i start the personalizing process, i havent done anything with that yet. i do remember having to use the custom and select the partition although

 

[USAFRet]

So I just recently built my new gaming computer, and so I found what I though was a product key on a website but it turned out to be like a developer preview or something, it was windows 8.1 pro build 9600, and always had a watermark in the bottom right saying "Activate Windows go to PC settings" and i tried it but I needed a valid product key. (Yes I used the windows media creation tool on my USB to get 8.1 pro) and so my neighbor got me a USB with a copy of windows 10 that I wouldn't need a product key (legal not a crack, dont worry) so I then proceeded to remove all of the files off my PC using the computer settings but was surprised when it was finished that it was back to the windows 8.1 setup screen. So I need to know how to completely remove EVERYTHING off of my hard drive, including the operating system so I can install Windows 10 now. Help much appreciated.... Thanks all!
PS. If you need to know I have a Seagate 1 tb hard disk drive

During the OS install, when it asks 'where', select Custom.
You'll see several partitions.
Select each one, and delete. Leaving one large space.
Let Windows install to that, creating what it needs

Do you mean while setting up the windows 10 usb? i cant get my computer to boot using that usb to start installing windows 10, instead it just boots to windows 8.1 that i already had installed, it takes me to where i start the personalizing process, i havent done anything with that yet. i do remember having to use the custom and select the partition although

No, when booting from the Win 10 USB that you create.
You're looking for a complete clean install of Win 10, right?

Boot from that Win 10 media, delete all existing partitions, and proceed.