I don't know the Prinz Jet Drum, but I use a Meteor Standard E, which should be the same in principle.
As was already said, you may place the paper face up or face down on the canvas. However, some drum dryers have an additional tension lever for high gloss (face to the drum). This adds tension to the rollers that press the canvas to the drum. The more gloss is desired, the more pressure is needed.
There are two principal parameters you must find out: temperature and speed. Optimal settings may vary with the paper you use. The optimum temperature is usually around 65°C (150°F). The speed is ok, if the paper peels off itself after one ¾ turn of the drum, usually with loud creaking. The louder it creaks the better, because louder creaks mean that large areas are coming loose at once.
If the emulsion cracks, your temperature might be too high (at least for the kind of paper you use) or you are using some force to peel the paper from the drum. I repeat: the paper must loosen itself. Some paper might need hardener and/or additional aids like Glanzol.
Replacing the canvas yourself is usually not easy but should not be impossible. Anyhow, you'll need some tools for doing that. Don't care too much for the condition of the canvas. Even if it does not look very appetizing, it takes a lot until it actually needs to be replaced. It is usually made of linen an can be washed in a usual washing machine.