you'll be lucky if its not rusted solid dude...... ive not yet done one where i havent either had to drill out & weld in a new lambda bung, or retap the thread.......
heres how i do it... there may be a million varaiations but this is mine,
before i raise the ramp i unplug the lambda,
raise ramp
unclip the cable & make a note of where it goes for refitting,
thread box spanner, or swan neck ring spanner through cable & undo....... I have the luxury of a lambda socket, however, this does tend to open up an sometimes slip so i prefer the above spanners.......
its at this point you will fight hammer & nail, skin your knuckles, resort to heating & bashing the old lambda untill its free.....
inspect thread, if all is well...
refit new one....
i wish you the best of luck.....