If there is pending litigation and your attorney remains the attorney of record, you will need to have your lawyer officially withdraw from the case. That may necessitate his filing a motion. You will owe your attorney for the time it takes to withdraw,

In the alternative, you can hire a different lawyer and have your lawyer prepare a substitution of counsel, which your former lawyer can sign and return. I don't know if your current/ex-lawyer will do that without charging you for his time, but the time involved should be pretty minimal.

If no litigation is pending, you can ask your lawyer to send notice to opposing counsel that he no longer represents you and to direct any further communication to you (or your new lawyer).