How do i cut my dogs nails? (HELP)?

ok so i have a bet hound beagle mix (mostly bet) named presley. His nails are super duper long! whe he goes to the vet they cut them but they are still really long, right now his nails are grown too the point where the curl over each other and he seems in pain! he doesnt like me tooo touch his paw he tries to nip at me! what do i do!