Technology changes constantly, and if you're not careful, your existing PC or laptop could become obsolete before it's time.With PC and laptop sales ranging from $500 to $700 on average, and up to $1500 for a Mac, the cost of an upgrade can be significant.But what if you didn't have to throw out your existing computer?The good news is, you might not have to. Here are 9 computer maintenance tips you can use to keep your computer running for longer.1. Clean Any Dust or GrimeLike…