Step 1: If one of your bars is broken, you need to get a new one. It's a one piece job, and unless you can weld, can't really be fixed. I bet you could score one at a junkyard for under $10.
Step 2: If you found a car that has the necessary bars, all you need is something long that can pry things well. You will notice that each "torsion" bar attaches at one end to the arm, then goes all the way across to the other end, loops behind the support plate, comes back in front of it, and loops once more into a one-of-3-slotted plate. Take your prybar and just pry the looped, hooked part. It will probably shift and go into the next slot. In other words, you may need to keep prying at it until it is free of the plate.
Step 3: Now, gently wrestle the bar out. You may have to experiment with different trunk angles to allow it to be free. Also, make sure to grab the (approximately) 1 inch diameter iron roller wheel, which attaches to the arm side.
Step 4: Now, reverse the process to install it. Fenagle the roller end in first and make the roller engage the arm. Get that prybar handy again and pry the looped end through, and thats all! No more using a 2 x 4 to keep the trunk lid open (I had to do this).