How do you replace the ECM on a 1991 Chevy Beretta?

To replace the ECM (Engine Control Module) on a 1991 Chevy Beretta, first disconnect the negative battery terminal to avoid electrical shorts. Locate the ECM, which is typically found under the dashboard or in the engine compartment, and remove any screws or clips securing it. Disconnect the wiring harness and remove the old ECM, then install the new one by reversing the process: connect the wiring harness, secure it with screws or clips, and finally reconnect the battery. Be sure to check for any diagnostic codes after installation.