We don't talk about piracy here but a laptop with an installed OS doesn't mean it's pirated. However it also depends on whether you buy your pc from random shops, retail shops or official flagship stores.
IF a pirated win8.1 supports windows update (means can receive updates from microsoft even though the OS is not genuine) then it can most probably upgrade to win10. Otherwise I have no idea, maybe you can also trigger manual download and upgrade too.

This post has been edited by lolzcalvin: Jul 31 2015, 01:18 PM