First you find one of the snorlaxes left of celadon and the other one is right of vermillion, then you use your pokegear radio (if you don't have it shame on you) and look for the poke Flute song. Talk to snorlax with the poke flute song in the background and he/she will wake up and attack you in a grumpy rage! Snorlax is an annoying Pokemon to catch no matter how good you are so don't be afraid to just run away, there is another one....
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Get the Pokemon flute from Mr.Fiji in Lavender town after you rescue him
Give them a Bitter berry, play the poke flute,or give them an awakening
After you get the pokeflute you turn it on and go to the sleeping snorlax and it wall wake up you will be able to fight it at level 50
The radio will be your instrument to wake up the sleeping Snorlax. There's a certain radio station that plays the poke flute. When you face Snorlax, tune in to that station and let the Snorlax hear the flute for it to wake up.
use the pokeflute but if ur in heartgold or soulsilver, move the dot on ur radio to the top of the circle (pokeflute channel)