Not sure of your model, but typically the distributor has a screw on a collar around the shaft where it enters the block.
Loosening the screw a bit allows you to rotate the distributor. With the timing light, and the engine running, rotate until the timing is set. Turn off the engine, tighten the screw, and recheck the timing.
One hint, I use a pair of those black chemical gloves that go to the elbow when I time my engine. I got tired of getting zapped!
