I have a thread on here about replacing the water pump, which involves all the exact same steps as replacing the timing belt. In fact, good practice is to go ahead and replace the water pump and belt tensioner, all at the same time, because hey, you're in the neighborhood
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It's late now and I'm blown out tired, but I can find that thread link for you. I think it's under What I Did To My Wagon Today. It's got lots of photos and comments, uploaded directly to FEOA, so there's no hosting site issues.
The process isn't particularly difficult, but it is time consuming, because of all the stuff you have to take out and move out of the way to get at the belt. (Hey, if you pull the engine out, it gets much easier,
). Basically you're going to have to undo the motor mount at the 'front' of the engine (passenger side), then either jack up the engine from below with a floor jack, or lift it up from above with a hoist.
You'll only need to lift the front of the engine about 2 inches (the other motor mounts will provide this much flexibility), and this is to provide clearance on the right side frame rail for taking off the crankshaft pulley. You'll remove the accessory serpentine drive belt, then remove the crankshaft pulley, then remove the black plastic timing belt cover. At this point you should be able to visibly see everything you need, and from here it's just an ordinary task of changing the belt.
It's STRONGLY recommended to change the belt tensioner, and again while you're in there, might as well do your water pump as well (unless it's like brand new or such).
The 1.9L is a non-interference engine, so the valves won't be damaged if the belt breaks during operation. But it's still not fun being stranded somewhere if it goes out.
Good luck!