Unless you are sure you know exactly what to do and how to do it, it would probably be wisest to hire an attorney to help you with this. Enforcements are tricky. If you don't do them exactly right and you lose.
Since you have a stipulation like this in your decree, you probably had an attorney for the divorce. Talk to him or her again and see if they think it is worth the time and expense.
For educational purposes only. No attorney-client relationship was created by this communication.