Verify that your current Windows 8.1 is genuine and activated under Settings > PC settings > Update and recovery > Activation . How to Download and Install Windows 10
If you are running original Windows 8, you must first upgrade to Windows 8.1 Update to be eligible for a direct upgrade path. can you download windows 10 on a windows 8 computer
Before starting the download, ensure your computer is ready for the transition: Verify that your current Windows 8