Things You'll Need
Instructions
Obtain an Eevee from a gentleman located in the Celadon City condominiums. Make sure you have an empty slot in your party because the Eevee cannot be transferred to Bill's PC. You will need to enter the condominiums from the back end and climb up to the top floor.
Trade your Eevee to either the "Ruby," "Emerald" or "Sapphire" versions. Head to your nearest Pokemon Center and proceed to the second-floor trade center. You will need to connect your game system to another Game Boy Advance console to begin the trade process.
Talk to the trade center attendant and select Eevee in your party to be traded.
Raise the Eevee in either "Ruby," "Emerald" or "Sapphire." By keeping it in your party and not in the storage PC, Eevee's happiness will rise and result in an eventual evolution.
Decide whether to evolve it into an Espeon or Umbreon. If you are playing and level up during the daytime hours, Eevee will evolve into a Espeon. If you level up at night, Eevee will evolve into an Umbreon. If you do not want to evolve Eevee, press the "B" button to cancel the evolution.
Repeat Steps 2 and 3 to trade Espeon or Umbreon back to the "FireRed" version. You will also need two Game Boy advanced versions to complete the trade-back.