EPA regulations dictate that you should take it to a shop and have the system evacuated. Basically they will identify what is in the system, suck it out, then you can remove the hoses and replace the compressor. Then you should have the system flushed, and a vacuum pulled. They usually will pull 30 inches of vac and let it set for 30 minutes to see if it will hold. If so then the system can be charged again.
To open the system and vent the freon into the air is a federal offense if you get caught, the jail time and fine is enough to make me want to do it the right way.
Actually to have a shop R&R the compressor for you should not cost that much, and you will know it was done right and should get some kind of warranty for the work.
Just my .02's worth.... good luck