After you get a sight of all 210 Pokemon, go back to the lab of Rowan and speak to Professor Rowan. Follow Oak to the new Pal Park, then go to the house near the Eternia Gym. Oak will then give you an upgrade
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If you trade a porygon with an upgrade it will evolve into porygon2 =0
well first you gotta get a porygon. then let it hold the upgrade. then trade it and you'll get porygon 2. trade again with dubious disc to get porygon z. Only Porygon needs Upgrade and you need that upgrade to trade for it to evolve. You need to trade it together with the upgrade for it to evolve.
Give porygon an upgrade and trade it it evolve it. And of course you have to trade it back. Try this in Pokémon go!
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.
To evolve it into a Porygon2, trade Porygon holding an Up-Grade. To evolve Porygon 2 into Porygon-Z, trade Porygon2 holding a dubious disc