You don't say what make or model of laptop you have but think you will find that the key is integrated into the bios. You might find the Certificate of authenticity (CoA)underneath the battery.
If upgrading from Win8 to Win 8.1 you shouldn't be asked for your windows Key.
Most new laptops have a program that lets you make a master copy of the software installed on your laptop, I know with Toshiba and HP laptops they nag you if you don't make these disks.
Have a look here for how to make a master restore disk 1=Performance">click here Maintenance
and here 1=Performance">click here Maintenance