Not only don't shift, don't press the clutch pedal if you are in deep water. The jeep should start in 4-low with out pressing the clutch if you happen to stall.
Take recovery gear, doesn't matter how easy the trail is, if you are stuck you are stuck. It happens to the best of everyone. Don't do anything your not comfortable with, remember they are not paying for your car you are. The trail will be there when you are ready to come back and try it. Don't try to straddle tall rocks, get a wheel up on it and go over it that way, the last thing you need is being high centered on it, or puncturing something important like an oil pan.
I heard this once before and I feel it needs repeating. If this is your first Jeep and you are new to wheeling, the only limiting factor you will encounter is your puckered ***.