Trade it while it is holding a Dubious Disc.
You will have to evolve a Porygon. By evolving it you have to trade it while it is holding an Up-Grade.
In Pokemon Platinum (I don't know about Diamond and Pearl), Porygon is located in a house directly behind the Pokemon Center. If you want to evolve into Porygon 2, trade it holding a Up-Grade, and if you want to evolve Porygon 2 into Porygon Z, trade it holding a Dubious Disk. I do not know where htese items are found. If you want to get Porygon the harder way, use Pokecheck.
Porygon can evolve into Porygon 2, while holding an Upgrade and traded. Even further, Porygon 2 can evolve into Porygon Z, while holding a Dubious Disc and traded.
if you give it to a porygon 2 and then trade it it will evolve into a porygon z to get a porygon 2 you must give a upgrade to a porygon and then trade it and it shall evolve!
Porygon evolves into Porygon-2 when traded while holding the item "Up-Grade".
You must evolve Porygon (From Celadon) using the UpGrade to Porygon 2.
If you mean how do you evolve Porygon into Porygon 2, you give it the Up-Grade item and then trade it. But if you actually mean evolve Porygon 2, you can't; Porygon Z wasn't introduced until Generation IV.
trade while holding up grade and it will evolve into porygon 2
That Would be Either Porygon or Porygon-2
its used to evolve porygon into porygon 2.to do that you have to have porygon hold it,then trade him.
Catch pokemon, battle, almost all the same stuff as the other games.
Attach the Upgrade to a Porygon and trade it to another game. It will evolve into Porygon2 when it arrives in the other game.