There is no easy way to beat the Elite Four. You have to level up your Pokemon and use the right types of Pokemon against each of the elite four (i.e. don't use a fire-type Pokemon against water-type. Use electric instead). I recommend level 60 or so for the Elites. Good luck!
No its not an HM in leafgreen.
train your Pokemon that's it.
Beat the elite four.
You have to beat the Elite Four once.
all you have to do is not get beaten
beat the elite four and your starter has to be a bulbasaur
The best team to beat elite 4 in Pokemon firered and leafgreen are the first six Pokemon you caught and trained
You have to beat the elite four and complete your pokedex.
The same you can do in Fire Red.Read my answer to that here:What_can_you_do_after_you_beat_the_elite_four_in_pokemon_fire_red
beat the elite four
you catch and train Pokemon fill up the pokedex and beat the elite four
u can beat elite 4 again ., but they has improve their pokemon level . GL !! ^^