Gary, LouisianaGuy covered most of the bases. If you do have to heat out the plastic wear safety glasses. Have had a couple of the units spit/pop the material out.If you do heat them out allow the metal to cool as you can bend the metal if you try to press or hammer them out of the hot units.Once the old joints are out apply a thin layer of grease on the Yoak and Driveshaft openings, this will allow the new cups to slide into the assy. much easier. Also use Joints with grease fittings and be sure to install the joint so the fitting is in the proper direction so you can grease it on the car with the shaft installed.
Double check your clips before you install the driveshaft and pivot both ends of shaft. If any of the joints are tight you may have dropped a bearing inside the cap. Don't forget to grease the new units.