When the computer is booting up, press F11 and Ctrl over and over. That takes you to a screen that can guide you from there
You cant restore every computer. It has to have recovery partition. And F11 and CTRL only works for Dell (I could be wrong, that's from memory) whereas Acer is CTRL/ALT F10 (again that's from memory). Different maker's use different key combinations, you will have to do a bit of googling. And again, this will only work *if* you have a recovery partition.