I forget to tell you a very good advice. Choose a model made of pvc uv ray proof and made with many insulating channel. Ask that to your sales rep. Also two lay of glass uv proof is excellent.
If your flange is in brass or plastic, you have to cut off the pipe under. Then you can buy a special flange, in your local home center or a plum shop, that goes into the pipe.
You must remove the front panel. Look carefuly, you must see small srews or clips. After you removed the front panel, the drum must slide. All the appliances are made like that. Then you go to your reparator shop and you buy what you need.