Only cut your dogs nails if you have a nice sharp dog nail clipper, and some quick stop available. And since you are obviously not familiar with it, I'd do what others said and only trim a tiny bit off at a time.

You would probably feel more comfortable having someone else do it. Is there any groomers in your area? Most will cut the nails without an appointment. Please don't let the nails go too long, as it is painful for a dog to walk on long nails.