How do I change my public defender?

Have you contacted you the supervising attorney in your PD's office? They may be able to work things out between you and your PD. If that's not possible, then ask the supervisor about changing PD's; this is known as "substitution of court appointed counsel".

If that's not an option, then you can request a hearing for a substitution. However, you will need to convince the judge that this is necessary. To seek such a hearing you need to write a letter to the judge and request a meeting with them. A copy of the letter should be sent to both the PD that you want removed and the prosecutor in your case. Make sure both copies and the original (which goes to the judge) are sent certified mail (you also need to keep a copy for yourself). The letter should state the reason(s) why you want your PD removed from the case (list all the problems that you are having). The letter should be short, to the point and truthful (you don't want to jeopardize your position with the judge by exaggerating things, etc).