How do you get the silver and rainbow wings in FireRed?

You can't get the silver and rainbow wings in FireRed. Those are exclusive to Pokémon Emerald.

In FireRed, you can only obtain the Rainbow Wing by defeating the Elite Four and becoming the Pokémon Champion. This will unlock the Sevii Islands where you can catch Lugia, the Legendary Pokémon who needs the Rainbow Wing to evolve into Ho-Oh.

There is no silver wing in the FireRed game.

If you're looking for those wings, you'll need to play Pokémon Emerald.