I removed mine from the top. I did not remove the fan, or anything else for that matter. You will want to replace the orifice tube and probabaly the accumulator as well . Then you will need new o-rings for the compressor if it didn't come with any, and the accum. Some PAG oil to refill the new compressor and some in the accumulator. Then a vacuum pump to draw down the system to 30Hg. If it holds 30Hg of vac. for 1 hr. then the system is leak free and you can proceed to refill w/ the correct amount of R-134A (2.2lbs IIRC). Check the book to be sure as you don't want to overfill it.
And no, gauges made for R12 refrigerant will NOT work w/ R134A. Different setup.