Now that they've grown so long, you'll need to be very careful re: how much you trim off this first time, to avoid hitting the quick. You'll have to trim, or have trimmed, a little bit at a time. I'd definitely take him to your vet to have them done. It's so important to keep them trimmed reguarly. Walking on too long nails can cause him pain and affect his ability to walk. Maybe the vet can show you how to do it Let us know how he did!