You do not need an attorney, but I would strongly recommend one. Your chances of coming out on top are affected by rules of evidence, rules of procedure, caselaw, understanding of navigation within your local legal system, and general legal knowledge. A proper analogy would be to ask where to find a medical dissertation of appendix removal and, having read it, attempting to perform the surgery yourself.
With that disclaimer in place, I can say that you would have to file a Motion for Enforcement by Contempt with the same Court that dealt with your divorce (I am assuming that at least one of you still lives in the same county in which the divorce was granted). Having filed the motion, you would then need to serve a copy unto your ex, and then attend the hearing for the motion. The Court, if having found that the ex is indeed in contempt, usually will give them a little time to rectify their behavior to satisfy the original orders, i.e. to pay the said bills. Punshiment for not following the original orders include fines and possible jail, but judges generally do not fine/jail on the first hearing unless the contempt is especially callous.You should then seek to set a follow-up hearing to touch base on whether or not the bills have indeed been paid, which you can "pass" (ask to take off the docket) if the ex indeed has. If not, at the follow-up hearing, the Court may fine/jail your ex for contempt.
If successful at proving contempt, you can also ask the Court to reimburse you for your legal costs.
No, you do not need an attorney. However, the best results are often obtained when represented by counsel. Often, if your ex is indeed in contempt, the court may also force your ex to pay the cost of your attorney to bring this matter back into court (assuming that your ex has the ability to pay given that he hasn't paid the bills that were already ordered).