I am assuming your Win 7 has SP1 installed. Yes ?
If not, go get SP1 ( service pack 1 ) installed first.
Use the following link to download the Media Creation Tool. Make sure you pick the correct bit-version.
http://www.microsoft.com/en-US/soft...?OCID=reserve_r_PostReserve_MediaCreationTool
After downloaded, run the tool and select Create installation media for another PC.
That will create Windows 10 ISO file.
Right click at the ISO file > click Mount > click Setup.exe.
Installation will begin.
This method will NOT require a product key.
This method will allow you to keep your files, settings and apps.
I used this method to install Windows 10 Pro and Home to 2 of my laptops.