Do you want to upgrade the OS from your PC from Window 7 to Windows 8. If so you have to buy a windows 8 license for your PC.
Your Lumia 625 has no Windows 7 but already windows 8 (out off the box) if you want to update it to the latest version you need the WPST or LSRT. How can I recover/reset/restore my phone software? - Microsoft - USA