Alright, the solution is very simple. I am assuming you want to do a fresh install of windows 10, however, if you simply want to upgrade your existing windows 7 to windows 10, you would use the same process.
If you want to do a clean install of windows 10 you will need to download the windows 10 installation media creation tool from microsoft. You will need a usb with at least 4gb of available storage (note: this usb will have to be dedicated to windows 10. Don't attempt to use a partitioned usb/portable hd because your files will be erased once the usb is created). Once you have downloaded the tool start it and it will guide you step-by-step to create the windows 10 installation. After the installation media is created, you simply need to boot into the usb drive when you start your computer. You will need to check your computer to see what button you press on the bios screen to show the available drives to boot from. You can also default the boot option to the usb in your bios settings, and then change them back to your hd later. Once booted into the windows 10 installation, just follow the steps and install windows. When it asks for a serial number, enter the one on the windows 7 sticker that should be somewhere on your pc. Once you're connected to the internet, windows will automatically register it with your computer, and windows 10 will be activated.
Here is the download for the media creation tool from the microsoft website:
Windows 10 Download
Note that instead of doing a fresh install, you can also select to upgrade windows. Just press the "upgrade now" button on the link above.
If you need some additional help, take a look at this webpage:
How To Clean Install Windows 10
Also, if your replacing your motherboard you might run into the issue that your windows 7 license is registered to that specific computer/manufacturer. You won't be able to install a copy of windows on a new build with a license that came with the a computer that you purchased from a specific manufacturer. If you purchased the windows 7 copy separately, you wont have any issues upgrading.