The easiest way would be to speak with your ex and have him agree to the move. You should have a plan as to how your son would visit with his father once you moved. If the father does not agree, you can file a request for modification in court. If the father files documents against you moving away, the judge will likely send you to mediation. There, you would have the opportunity to explain why the move would be good for your son, and the father would have the opportunity to explain his position as well. If your moving will result in better resources and opportunities for you, it shouldn't be a problem.
This response is informational only and is based only on the information provided in the question. These matters are very fact-specific, and the response may change based on the specific facts of your case. This response does not create an attorney-client relationship or any continuing to duty to provide legal advice. If you require further assistance, plase contact an attorney at once.
There are two ways to seek approval for a move away in your situation, one is to petition the court, and the second is to obtain your ex-partner's approval. Certain legal processes have to be followed in both cases. The court will look at a number of factors in determining if a move away should be grated, including the amount of time your e-partner spends with the child, the benefits of the move versus the disadvantages and possibly a new visitation order that would still allow contact between your ex-partner and your child.
The answer is based upon the limited information provided and does not create an attorney-client privileged relationship.