Cleanest way to install on a new laptop.

Hi. This has probably been asked elsewhere but i can’t find it!. If so sorry for repost?. I have a new laptop with NIS preinstalled but unopened and a spare 3 system key. What is the best/cleanest way to install on the new laptop?. Open and use key, download and install over preinstall or uninstall preinstall and install from download. Cheers. Grant.