You should move the puppy pad to the back door and then start taking your pup outside everytime he is fed, have a tasty treat ready , a bit of cheese or something and as soon as he's done a wee/poop outside give the treat and loads of praise, it's a pain in the ass at first- specially when it's cold but worth it.
Look out for your pup getting ready to use the puppy pad, and if you catch him in time pick him up and get him outside quickly - then loads of praise again... once he picks up on this start moving the puppy pad outside the back door.
He should soon learn that the back yard his his terriotry and his place to 'go'
