Change 30 amp to 20 amps

sure if you want.

Whoa, there sparky!

Do you think you could flesh out that question quite a bit more, please.

You cannot just change the breaker amperage because you want to. What is the load on the circuit that you want to change?

Simple question, WHY? Maybe then we can help but your question is a bit too vague.

Question is Vague, more info would get a better answer, No problem reducing the Breaker Size, as if wired correctly and handle 30 Amps, will sure handle 20. The're times you may want to reduce breaker to reduce damage from overcurrent.
Or if you were converting an unused 30 Amp circuit to a 120 Volt Receptacle circuit.
Can you tell why? Thanks