make porygon hold and upgrade and then trade it.
Edit:::
That Is One Way, The Other Way Is to Have It Hold The Up-Grade And Level It Up.
Ah hah, i can answer this one. You need a data disk which is produced by silph co. first, then you give it to a porygon and trade it to something. DO NOT MIGRATE ON DIAMOND OR PEARL, it won't work as it isn't the same as trading.
Hope this helped!
** The 'data disk' mentioned above is called an Upgrade.
Which you can find in i think cerulean cave
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Used on porygon to evolve to porygon2
This item can be found in the game it can be used to evolve a Porygon to Porygon2 by trading it to someone.
In order to evolve Porygon into Porygon2, you must give it the Upgrade item and then trade it to another game.
It is impossible to obtain a Porygon2 without trading. You can get a Porygon and trade it with an Up-Grade or you can get a Porygon2 from the GTS but there is no way to get Porygon2 without trading.
Porygon2 is a 2nd gen pokemon and does not appear in Pokemon Red. That aside, both of Porygon's evolutions occur when you trade it while it holds certain item. Up-Grade for Porygon to Porygon2, and Dubious Disc for Porygon2 to Porygon-Z.