As I wrote about before, Windows 10 will be here soon – July 29th to be exact. In the meantime, you may have notice a new icon on your menu bar. By clicking that icon you can reserve your free upgrade. Read about the process here.
If by some chance you do not have the icon, Microsoft explains your options here. The first thing to try is to install all the latest Windows updates for your version of Windows, hopefully 7 or 8.x. (If you are still on XP, please, please, please speak to me about your options. Your computer is not safe on XP any more.)
If updating Windows does not cause the icon to appear, doing the other suggested steps are rather complicated and I do not recommend you doing them on your own unless you fully understand the instructions. You will have a chance after July 29th to get the upgrade.