If you look straight down from above at the back of the engine, between the engine and the firewall, you can see the sensors. They are vertical. The wiring connects to a green 4 spade connector on the firewall on the RHS and brown on the LHS. (You can verify you have the correct connector because there will be 2 white wires, 1 black and 1 grey).
To access the LH one:
Loosen the coolant expansion tank. Philips head screw right front. Tilt front up and slide back. Remove coolant pipe connection to the tank up by the firewall nd and plug it with somethingto avoid spillage. Twist coolant tank out of the way. (The other pipe and sensor underneath can stay connected)
Pull the brown connector off the flimsy plastic bracket. (The bracket often breaks) Disconnect the sensor from the connector and free up the wire. Now you can reach the sensor, thru the gap to the right if you push the wires and pipes out of the way.
Use an Oxygen sensor socket to push down over the top of the sensor and unscrew it with a long extension and swivel joint. (I tried getting a wrench in there but there's no space to turn in it.)
On the RHS:
Remove the air filter concertina pipe. Disconnect the green connector and free up the sensor wire. Make some space by removing any cable or pipe ties so you can insert your hand down behind the valve cover to the sensor and get the O2 socket on the sensor. Unscrew it just like the LHS.