Allow Rhydon to hold a Protector, then trade it with someone. It is recommended to ask a friend for a trade-back to ensure your new Rhyperior's arrival.
you have to trade
Basically Rhydon doesn't evolve on a certain level. You need to have Rhydon hold a Protector and Trade it, with a another person.
you have to trade it with a certain item
Rhydon evolves when you trade it while holding the Protector.
you cant evolve rhydon in fire red because the "protector" wasn't incorperated into the games until diamond/pearl
On Pokemon Diamond the Protector is a hold item for Rhydon. It is required for Rhydon to evolve into Rhyperior when traded while holding the Protector.
You cannot get the protector to evolve Rhydon in Pokemon Red version, because Rhydon's ability to evolve with a protector into Rypherior is only available in the latest versions: Pokemon Diamond, Pearl, and Platinum. It is impossible to even get a protector in Pokemon Red version, let alone evolve Rhydon.
Trade it when it is holding a Protector. In Diamond and Pearl, this is found on Route 228.
Rhyhorn evolves into Rhydon at Level 42
A Protector, when traded with Rhydon, will evolve it into Rhyperior.
Rhydon will not evolve in leafgreen or firered you have to migrate it to diamond, pearl or platinum then trade it to evolve it.
make rhydon hold the protecter and trade it then it will evolve