If establishing a retirement fun, then moving to a different state, which state would determine tax level?

I will move from Calif. to a mid west state. Tax tables are lower there. I will be accessing my retirement account. I want to know in order to be taxed on the funds at the lower tax level of that state do I have to move funds, or do I simply change residency. Is there a time frame needed to facilitate the change and insure the lower taxation?