No need to create partitions, the Windows 10 installer will do that for you, if needed. Just delete the current Windows partition after booting from your favorite partition manager (there are many free ones), and then install Windows 10 from the medium made by Microsofts Media Creation Tool in the empty space (I advice 128 GB at least).
In fact, you don't even need to delete anything. If you use a third party utility to mount the iso-file you download, you can run setup.exe from Windows 7, and it will install Windows 10, without even asking for a license code.
However, we really recommend to install Windows 10 on a new SSD, not on the old HDD. Much faster.

The OEM license code might not be valid on a new machine. Then you'll have to buy a new licence for the new machine.