Magneton is a Pokemon that can be found in the Unova region. It evolves from Magnemite at level 30, and can then be evolved into Magnezone by leveling up in a magnetic field.
In Pokemon White 2, there are two ways to evolve Magneton into Magnezone. The first is to find a magnetic field and level up Magneton there. The second is to use a Thunder Stone on Magneton.