how can i change the guardian ad litem

Your message is confusing; the father of your son is living with you? Why would you need to take him to court if you two are living together? If that is not what you meant in your post, but instead, you meant to say that your son is living with you and the father is not helping with  the  bills, you can file an action to compel him to pay support. If you are not married to the father, you would have to first file an action for paternity. Once paternity is established by DNA testing, they can set custody orders, including an order that the father pay child support. If you are married to the father, you would have to file an action for legal separation or divorce and request an initial court hearing; at the first court hearing, they can establish custody, visitation and child support orders, among other various financial orders that the court may need to deal with in your case.   On the second issue, which is whether you can change the current court appointed guardian ad litem, that is very difficult to do as the  GAL is hand picked by the trial judge.  Litigants who are unhappy with the recommendations of the guardian ad litem routinely argue or advcoate that they want the guardian ad litem removed from the case. I have been practicing  for 33 years and have yet to see a judge remove a guardian ad litem for cause. It is doubtful that the court would do so in your case.