You can't. The name rater won't change names for Pokemon that someone else named... only for Pokemon that you named yourself. This is also true for Pokemon that you traded from another game... any other game, even if it was you playing it, the game can't tell, and so the names are permanent.
You can rename a pokemon by going to the Name rater
You can rename pokemon when you first obtain them or ask the Name Rater to change it. The Name Rater is in Lavendar Town he's in a house below the Pokemon Center. Bring the pokemon you want to rename to the Name Rater then he will let you rename it. Keep in mind pokemon obtained through trade cannot be renamed.
There is a name rater in Castelia city.
you go two the name rater in the town where the Pokemon tower is
you go to the name rater's house. but if it is a trade Pokemon then you cant rename it.
You can rename a pokemon by going to the Name rater
You can rename pokemon when you first obtain them or ask the Name Rater to change it. The Name Rater is in Lavendar Town he's in a house below the Pokemon Center. Bring the pokemon you want to rename to the Name Rater then he will let you rename it. Keep in mind pokemon obtained through trade cannot be renamed.
The Name Rater will rename any of YOUR Pokemon. If you own a Pokemon that originally belonged to someone else (Like the Machop you trade for in Goldenrod), then he wont rename it.
In slateport city there is a name rater who can rename your Pokemon remember Pokemon traded to you can't be renamed.
There is a name rater in Castelia city.
Go to the Name Rater in one of the cities.
you go two the name rater in the town where the Pokemon tower is
you go to the name rater's house. but if it is a trade Pokemon then you cant rename it.
You should go and find the Name Rater, then rename it back.
Go to Lavender Town, the one with the Pokemon Tower. There should be a house where you can change your Pokemon's name. There should be a sign near the house saying Name-Rater. you go to Lavender Town and look for a house that says Name-Rater
There is a man in Slateport that will change your pokemon's name.
There is a name rater in Castelia city. In a building just go on the street diectly east of the Pokemon center