1992 Lexus SC 300 Recharging

Air Conditioning problem
1992 Lexus SC 300 6 cyl Automatic 275, 00 miles

I am a single 57 year old women who is pretty mechanically savy but do not know on this particular car how to recharge my air conditioning unit so it cools the air again. What type of product do I need to purchase and where do I put the additive in? Do I need the individual cans of cooling additive only or the whole package with the tubes and values and stuff. The air compressor is just fine and the fans and such its just not cooling the air much like it used to. Thanks for doing this! It is a great help for individuals like me to have this as a resource.