Air/fuel sensor replacement

I own a 2001 Toyota Tundra, V6, 24 valve, 2 wheel
drive automatic with 73K miles. The dealer told me the O2 sensor that is located before the catalytic converter is bad and needs to be replaced. I took it out but the sensor doesn't seem to disconnect from the small gray plastic connector the wires are attached to. The wiring from the sensor seems to join another set of wires that form a sort of "V" and then continue on up the engine compartment. I didn't want to force the wiring from the plastic connector, but I don't see any way I can disconnect the wiring so I can repalce the sensor. Where does the wiring disconnect from the sensor so the sensor can be connected. I haven't purchased the new sensor because I am not certain if I can do this or not. Please tell me what you can about this problem.