The upstream sensor is located in the exhaust manifold over on the right.

The downstream lambda sensor is located in the middle of the exhaust can.

Follow the wiring to the connections and disconnect before undoing the sensors.
These can both be removed using a 22mm spanner and they spin out in an anticlockwise direction.
It is always a good idea to spray them with PlusGas before removal to free them a bit.
Also, a dab of copper grease can save them from seizing up next time.
On refitting, retighten the sensors to 40Nm if you have the correct tools.
If not, just make sure it is tight, you don't need to swing on the spanner though.