Look at your new part. You will see an allen down from the top and a wrench like protrustion on the bottom. When you adjust you place your allen wrench into the top female allen socket and you push against the light spring untill the allen on the bottom of the tower engages its female receptical and then you turn it.
If you were doing all that I fear you have a problem with the lower screw rather than the tower. The tower comes with break-off screws which must be chiseled out of the old set-up. There are threads beneath what you say look like rivets. We usually break the tower off and pull the pieces from beneath the one time screws. They then come out with a pair of pliers.
[This message has been edited by stevebfl (edited 11-16-2000).]