there is special equipment needed to do an air conditioning compressor unit. the tools required will make it a job best left to a professional or at least someone with the tools . installing the pump is simply a matter of removing the bolets holding it on and putting the new one in also removing the to hoses and electrical connectors. thats the easy part once you put it together you have to purge the system of moisture by pumping out the air so you will need a vacuum pump . you will also need to replace the condenser. whenever you open a air conditioning system you need to replace this . Once youve purged the moisture you need to test to see that theres no leaks in the system and only then if theres no leaks will you be able to put the freon into the system . This is a very informative video
https://www.youtube.com/watch?v=95RdGLFIbL8