Which key should I use?

Hi!
I have Samsung laptop that came with preinstalled Windows 7 Home Premium (64-bit). I have COA sticker on bottom of my device too. I use ProduKey to check my Windows 7 key but it doesn't match to my key on COA sticker. Furthermore I checked this key from ProduKey in Google search and I found him . Is it normal?

So with key should I use to update my device to Windows 10? I want to replace my hard drive so I need to install Windows 7 on my new hard drive and then update to Windows 10 or just download Windows 10 Home TH2 ISO and use key from Windows 7 to fresh install Windows 10? Which key should I use?

English isn’t my native language, so please excuse any mistakes.

You want to use the product key from the COA sticker. The other product key is called OEM:SLP - system locked pre-installation. The OEM:SLP product key activates Windows based on licensing information contained in the factory load of Windows (and the manufacturer's recovery discs) and cannot be used to activate Windows installed from a consumer source. The manufacturer uses this so they can load the exact same Windows onto thousands of computers without having to uniquely activate each one. They provide the COA sticker with a unique product key so that the user can re-install and activate Windows from a consumer source - such as an ISO file from Microsoft.

Thank you very much for you reply. So, I don't have to install Windows 7 again on new hard drive, right? Can I just put Windows 7 key from my COA sticker during Windows 10 TH2 installation?

Thank you very much for you reply. So, I don't have to install Windows 7 again on new hard drive, right? Can I just put Windows 7 key from my COA sticker during Windows 10 TH2 installation?

You should be able to. You have to install the version/edition of Windows 10 that matches the Windows 7 product key. The COA sticker should say what version of Windows 7 it is for. More than likely you are going to want to install just plain Windows 10. Not K, not KN, and not Single Language. Just plain Windows 10. The plain Windows 10 download from Microosft will contain both home and pro versions. When it asks you for a product key during installation you want to select whatever option is presented for skipping it. The first option is "I don't have a product key". Later options might be "Skip" or "Do this later". It will then ask you if you want to install Home or Pro and you pick the one you have a product key for.

After you get Windows 10 installed then go to settings, Updates & Security, and the activation tab. Click change product key. That is where you manually enter your Windows 7 product key to activate the Windows 10.

A much more reliable method of upgrading to Windows 10 by the clean install method is this:
Clean Install Windows 10 Directly without having to Upgrade First - Windows 10 blog

Make sure to copy the genuineticket.xml file to an external storage - you can even just put it on the Windows 10 USB flash drive if that is what you are using to install Windows 10. Between steps 6 and 7 in the tutorial you would replace your old hard drive with the new one.

OK, thank you very much again for your very helpful replies. Unfortunately I can't give you reputation points because I must spread some reputation around before giving it to you .