How do you let the previous producer know that he/she can no longer be involved with the song? You tell the producer. There is no other way of getting around it.
What are the ramifications, legally, for you if you make that move?
You could get sued, if there is something to fight about?
What is there to fight about?
Intellectual Property - Copyright Law:
1. Who owns the lyrics and vocal melody created?
You say you do. Fine. Then you should be able to move on with the copyrights you own exclusive to you and work with your new producer. However, just because you say you do doesn't mean the producer will say the same.
2. Was a joint work created when you and the producer worked on your song three years ago?
This is the critical issue here and where artists and producers typically have a major issue.
If you create work with another artist and each of you prepared your contribution with the intention that it would be combined to create a single work, then that work is a joint work. The contribution needs to be more than a minimal.
If the foregoing criterions are met, then the work is jointly owned by both of you and each of you share in the ownership of the entire work.
This is usually were it gets tricky and messy. Accordingly, to get out of the mess, you look to the music collaboration agreement you signed spelling out your rights and responsibilities. You did sign one, didn't you? If the answer is no, then it just means headaches are ahead because this producer will most likely not be happy that you are cutting him/her out.
In short, get a lawyer.
Best wishes with your legal matter.
-Uduak Oduok, Esq.
Ms. Uduak Oduok is an attorney with EBITU LAW GROUP, P.C. The information she provides here is general information. Further, it is strictly based on California law. NOTHING HEREIN FORMS AN ATTORNEY-CLIENT RELATIONSHIP NOR SHOULD BE CONSTRUED AS LEGAL ADVICE. For a legal consultation on your matter, you would need to contact her office directly at www.ebitulawgrp.com.
You don't mention what your agreement (if any) with the original producer says; if there is a written contract, you need to follow that. There is a larger question of who owns the original recording, and I'm assuming you own the copyright to the lyrics and melody (and didn't assign it to the original producer). You need to seek a consultation with a lawyer who knows intellectual property who is in your area. Use Avvo Attorney Finder function.
This answer does not create an attorney-client relationship. It is not legal advice. Please contact a lawyer qualified in your jurisdiction to discuss your situation in confidence, using your factual details. Avvo answers are only general legal responses. Item 9 of Avvo.com's Terms and Conditions are incorporated in this disclaimer as though it were printed here.
I wholly agree with the excellent response of my colleague. You need to review any writings between the two of you with an attorney. Regardless, if you are planning on doing this as a living, you really should have an attorney to review the situation to make sure you own the rights to your lyrics and melody and that they are filed with the proper entities.
I don't think you will receive any actionable advice here because it will require a proper analysis of all the facts and circumstances.
I suggest that you consult with a lawyer in private and discuss your objectives and options in more detail. You can start by calling around to several for a free phone consultation, get some insights then pick the best fit to work with.
DISCLAIMER: this is not intended to be specific legal advice and should not be relied upon as such. No attorney-client relationship is formed with the law firm of Natoli-Lapin, LLC on the basis of this posting.