Installing Windows 10 is an easy thing. First, you go to Windows and purchase the software if you haven’t already. Their free trial ended a while ago, so I’m sorry to tell you that you can’t upgrade for free as of the time this answer was written. Once the software and everything has been purchased, you can download it and follow the on-screen instructions to safely install Windows 10.
Basically, it’s like you’re installing a computer game or something for the first time. If you follow the on-screen instructions and don’t mess with it too much while it’s installing, you’ll be good to go. This is probably the best advice one can give, so if you have any other issues installing it, take the issues to Windows directly. They’ll know much more about how to properly install the product.