On pokemon crystal how do u get past the guard at silph co in celadon?

Question

On pokemon crystal how do u get past the guard at silph co in celadon?

Answer 1

You can't go any higher than the first floor of Silph Co. in Saffron City. Inside, the guard will give you the Up-Grade item needed to evolve Porygon, but is all that the building is used for now.

This follows with the trend that GSC takes place 3 years after RBY. The main character, Red, has defeated Team Rocket in the Silph Co., and now security has been stepped up. There's no longer a threat, so there's no longer any reason to go upstairs.