As the other experts have advised, you should keep your windows product key for the program you have on your computer now.
As far as I know ,if you want to delay installing the program, you have to indicate such, when microsoft notifies you that the program is ready to install. i don't know what updates Microsoft is installing to prepare your computer for the upgrade, so I would advise you to type FAQ about Windows 10 upgrade in your search engine and hopefully your questions will be answered.