You have to remove the lock to get to the hex shaped housing, to tighten it.
I just went through this and it is a royal pain in the a$$ to get that lock tumbler out. The best chance is to follow the pictures posted on it. Do a search and you'll find them. I think it was a Team Chev link.
Make the little coat hanger tool, it's needed and it works. I made an additional tool. Another coat hanger tool that is mostly a straight shaft. First, for a quick tour, go to How Things Work, do a search and read the how locks work. This helps while trying to imagine pulling the lock.
The one thing the other messages do not mention is while you use this little tool to hold down the one tumbler at a time, the act of holding down the tumbler is also holding the lock assembly, which is stopping it moving out. (The lock assembly is spring loaded.)
This is where things get frustrating. You need to hold the tumbler down so the lock can pop out (under spring pressure) but by holding it down, the spring can't push out the lock.
The answer is to take the other tool, a straight piece of coat hanger and go in through the very back of the lock assembly. You'll see a notch and the spring will be visible. While holding down the tumbler, push the back of the lock assembly and it will pop past the tumbler you're holding, to the next tumbler. As far as touch goes. It's a light touch to hold down the tumbler, a slightly heavier touch while pushing at the back of the assembly. You're just giving the spring a little extra push but I found that it was taking FOREVER until I did this.
Repeat. I think there's five that will need to be held down before it's out.
Put a masking tape mark on the lock and the door so you install it to the correct postion. (Don't ask.)
Rick.