Disconnect the electrical supply to the cooktop. Unplug the range from the wall outlet or flip the corresponding circuit breaker switch to the "Off" position if you have a stand-alone cooktop.
Examine the edges of the glass cooktop to locate the screws securing it to the range or countertop; the number and type of screws varies by brand and model. Remove the screws and reserve them for reassembly.
Pull the cooktop forward and disconnect the wiring. Pull the plastic wiring connectors to separate them from the wiring harness; the number of wires may vary by cooktop model.
Remove the cracked glass cooktop panel. Carefully dispose of the damaged glass to avoid injury.
Set the replacement glass panel on the edge of the cooktop frame; have someone hold the panel to prevent it from falling, if necessary. Plug the plastic wiring connectors into the wiring harness.
Slide the replacement glass cooktop panel into the cooktop frame. Replace the screws used to secure the cooktop to the range or countertop. Restore the electricity to the appliance.