Purchased an open-box Dell laptop from Best Buy, how do I do a fresh install?

I just purchased an open-boxed Dell laptop from Best Buy Dell Inspiron 15 i5559-1347SLV for $409 for my son, he's 6, first laptop. He's going to love Santa. Anyways, I assume that Geek Squad wipes everything before selling it again? However, is their a way to do a fresh install, a reset or whatever you want to call it? I want it back to factory settings.

Windows 10 was preinstalled. Will I need to purchase a Win10 CD to start over? I want the hdd wiped clean, nothing left over, especially any Dell bloatware. I'm not tech savvy with laptops but their is only around 800GB of space left on a 1TB hdd. I know Win10 takes up space but this seems a little much. I have to do this tonight before I wrap it up.

Another dumb question. After I do the reset how do I properly back up Windows in case of a crash, etc.? I have a PC that needs a safety net as well. I have no idea how to back up my PC and now his laptop. Yes, I know it's sad. I just remember back in the day, I had to burn like 10 DVD's do to a backup. I have no idea what method is most highly recommended today & how to do it.


Thanks guys & Happy Holidays!