You are entitled to cancel a contract with a lawyer at any time. If the contract provides for hourly fees, then you will be liable for the fees and costs incurred. If the contract is a contingency based fee, then the lawyer may be entitled to a portion of any recovery depending on the work that the lawyer has done since you retained the lawyer. You may wish to discuss with the replacement lawyer (or another lawyer) your liability to the lawyer you initially retained.
First thing to do is to tell current lawyer, in written form, to stop work. Current lawyer will be eligible for payment for all work done on your behalf until you let them know that they should stop. At the time you tell them to stop, ask for copies of everything in your file that was not a document you gave the lawyer. This will help you to know what, if anything, they have done to date on your behalf. You are entitled to copies of all such documents.