The Pentium D is actually a dual core based off two single core dies. Upgrading doesn't necessarily mean that, but what I can tell you is the performance difference between the two is worlds different - after putting in something like an i5 to replace your current processor it'll feel totally different, and the numbers it can output will be totally different. As I said, your machine can't take the i5 - your motherboard doesn't support it, and chances are your case can't mount it. You'll just have to scrap the machine & pull your data off it, and move it to a new machine. The only thing you might be able to save is the hard drive, but even that isn't worth recycling in my opinion.