Shut down -
Start - Power - Shut down

Well a colleague at work upgraded last night and his machine then had problems. BUT - he is a very geeky guy and goodness knows what his machine contains. It did work but just need more work and may have something in start up that was stopping it

Your problem with moving from Win XP to Windows 10 is probably not the freeness of it (you can just download the image and install) but rather whether the machine is of a high enugh spec and has sufficient memory. A lot of machines with XP are limited to 512mb RAM and I think that would be insufficient. As you can't UPGRADE from XP but need to reinstall you would need to make sure you backed up everything and re-installed all your programs etc

I bought a new laptop for my wife recently (actually a refurbed one) for £167 so perhaps it is time for a new one and leave the old stuff on XP