30,000 miles max before you should change it.
Stock A/C Delco replacement is more than good enough!
Newer ones have a fitting on one end and a push in lock on the other end of the gas line. You need to hold the line forward and you pull back on the botted end. Have a pail ready for excess gas uder pressure, but I find local garages when not busy will change one out for around $25, and for the possiblity of getting it into your face, eating your driveway away, good cheap insurance even though DYI is cheaper.