To access the washers door lock assembly, you can either enter through the door or the top of the washer. To go through the top you need to remove the three screws that hold the top down, these screws are located on the back edge, once removed the top will slide back and off.
Open the door to the washer and remove the screws that go through the front into the door lock assembly. Once removed reach down and pull the door lock up. In hand remove disconnect the wire harness one at a time. There is a little plastic piece to depress down pull out once disconnected.
Now take the new lock assembly and connect the wire harness and reinstall back to the inside of washer. Install the top back onto the unit and test for proper operations.
This Frigidaire door lock removal can be costly to have a technician out to repair. The local Frigidaire appliance parts house should stock one of these as it is a fairly common issue in the industry.