Dear Macrumors members, I'm using a Macbook Pro 13" i7 (Mid-2012). Originally it was purchased by a guy who never used it. I'm pretty sure he downloaded this version of OS X from the internet instead of paying for it. I'd like to clean install the Mac, because some applications like iPhoto and iMovie still pop up with questions about his account although I deleted it, and I have problems updating that software. I'd like to purchase Mountain Lion OS X from the Apple store for the small amount of 17,99. I'm not a computer expert. What is the best way to handle? Thanks in advance for all the advice!