changing oil cooler
 

how simple / difficult is it ?

is there any problems or any thing i need to know about, airlocks bleeding it through etc.

or do i simply undo one and fit another

easy job.
undo one, bolt on t'other. There's a couple of different types of connection available tho so make sure the unions are right on the new one.
No bleeding needed, it'll refill itself when you fire the engine, just check the oil level once you've run it for a bit.

thanks pal