Retrofitting 87 F-150 Lariat

How hard is it to buy the $50 retrofit kit and and drain the old freon and install the new kit?

why do you want to drain an refill if it is working if not it is probaly drained you just buy kit an refill but if the freon is gone you will need find the leak or you will just loose the new you put in as far as draining the old you need to get somebody that is certafide to recover the old freon an pump the system down