No need to change the damper unless there is a specific reason to do so. Check it when it off the car, there should be no sign of fluid leaks and when depressing the piston it should move freely and eventually return to the top. It is best to replace both sides but if you are trying to do it as cheap as possible then you could get away with doing one side.
You will need a spring compressor to get the assembly apart unless it has completely snapped in two and is under no tension any more. If you do need to compress it be careful and make sure you compress it below the break.
I have the workshop manual if you want to PM me your email I can send the pages over.