2001 Focus SE Air Conditioning

I have a 2001 SE and the A/C is blowing out hot air most of the time. Sometimes it blows out cold air like it should be it's acting like it's due
for a recharge. I've looked around online and the place to recharge it is on the passenger side front wheel well. I've found online the r134a for under $10 and am wondering how to actually do the procedure and what else I will need.
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