You have the legal right to terminate your attorney at any time during the handling of your claim for any reason or no reason. However, you should have another attorney lined up before you do so, as your statute of limitations could be coming up, meaning that a lawsuit would have to be filed. If you case is already in litigation, then the court will have to approve your termination.
As to the fees, the attorney is entitled to reasonable compensation for the hours that he/she spent working on your file from the time it was opened until the time of termination. It is not based upon any contingent agreement you signed with him/her.
Best of luck to you.