Gathering Multiple Eevee
Breed a single Eevee with a Ditto in the Pokemon Day Care Center to create more Eevee. Drop off the pair of Pokemon at the Center and check back later to receive an Eevee egg. The Eevee egg will hatch after you have taken a certain amount of steps while adventuring. Each Eevee will be used to earn another evolution.
Vaporeon
Use a Water Stone on an Eevee to change it into a Vaporeon. Vaporeon is a water-type creature known for its aquatic attacks including Aqua Ring and Acid Armor.
Jolteon
Apply a Thunder Stone to an Eevee to evolve it into a Jolteon. The electric Pokemon Jolteon uses a unique combination of moves such as Pin Missile and Thunder Fang.
Flareon
Expose an Eevee to a Fire Stone to turn it into a Flareon. Flareon, the Flame Pokemon, is an excellent user of fiery attacks like Fire Blast and Lava Plume. All of the elemental stones needed to evolve Eevee into Flareon, Jolteon and Vaporeon can be bought at the Celadon Department store.
Umbreon and Espeon
Trade Umbreon and Espeon from "Pokemon Ruby," "Pokemon Sapphire" or "Pokemon Emerald" to complete the collection of available Eevee evolutions in "Pokemon FireRed." Because "Pokemon FireRed" does not have an internal clock feature, you cannot evolve an Eevee into the time-dependant Espeon or Umbreon. In one of the other Game Boy Advance games listed, raise Eevee's happiness level by walking with it, giving it expensive vitamins and refusing to heal it with bitter-flavored items to evolve it. If Eevee is very happy and you level it up during the day, it will become an Espeon. If you level up a happy Eevee at night, it transforms into an Umbreon.