You do not need the disk. The disk is only for reinstalling Win 7 if you don't like Win 10.
Make sure your Win 7 Pro is SP1 installed.
You will need update KB3035583 installed via Windows Update.
Once that is done, you will see a Get Windows 10 icon at the system tray area.
Click open it and you will see the reservation for win 10 upgrade.
Fill in the info and your are done.
When July 29th comes, you will be notified that Win 10 is downloaded to your computer and you will have a choice of when to install it.