Legal Question in Criminal Law in California

That depends on many issues, including whether the case was a felony or misdemeanor, how long ago you entered the plea, whether you have already been sentenced, if you were represented by an attorney, if there is new evidence, or if there are possible immigration consequences.

Generally, it is very hard to withdraw a plea unless you have a very good reason. Most courts do NOT consider "I thought about it, and I changed my mind," to be a good reason.