Welcome to Gaia! ::

Well, in order to move the snorlax, you have to go through a tedious sidequest that involves heading to the power plant that's south of Rock Tunnel (you'll need to use surf to reach it), helping them find the missing Machine Part (Which if you've beaten Misty, you've probably done already). If You've already found the part, just head back to the Power Plant and give it to the chubby guy in the middle. He'll hand you an item and you leave. Then you head to Lavender Town's Radio tower and nab the EXPN Card from the director there. That will next you the Poke Flute. Head up to the Snorlax, switch on the Pokegear, head to the music section and put the tuner up at the very top. You should hear the Poke Flute music. Exit out of the Gear menu, then examine the Snorlax. The battle begins! You can catch it or beat it (or just run, though catching it is preferred if you never nabbed Fire Red or Leaf Green), then you head up through diglett's cave, exit, use cut on the tree, head up, and you should be in Pewter City!

If you haven't done this, I assume you actually have 3 badges left to nab, as you can only get to cinnabar island (and thus, the seafoam islands) from pallet town, which you can only get to by doing all of the above. Hope that helps!