To evolve Magneton into Magnezone, you'll need to be around a Magnetic Lure Module placed on a PokéStop. Once you're in its range, you can evolve it using 100 Magnemite Candy. The prompt to evolve your Magneton will turn green from red once you can evolve it.

How do you evolve Magneton into Magnezone sword and shield?

Magneton evolves into Magnezone when the player increases his pokemon's rating to level 30. The pokemon also evolves when it is exposed to a Thunder Stone.

How do you evolve Magneton into Magnezone in Hgss?

The only way to get a Magnezone in HeartGold and SoulSilver is to trade it to Diamond, Pearl, or Platinum, evolve it, then trade it back to HeartGold or SoulSilver. Both systems will need to be physically nearby in order to trade.