Change their cries? I hope you're asking for a simple "cleanup", not a radical change. More than 10 years after the Generation I and II Pokémon games were released, the Pokémon cries from the earlier generations have long since been able to define the Pokémon themselves.
Hypothetically, let's suppose that when Nintendo made the first Mario game, they didn't have enough memory for a long name for their player character, so they stuck with the short name "Mario". Asking for changing the Pokémon cries just because they were generated with older technology (I'm not necessarily saying that's your reason, but many other people cite that reason for wanting the cries to be changed) is like asking Nintendo to make Mario's name longer just because they now have the memory to do so.