I have a troy-built lawn tractor I need to take the pulley off the shaft to take the belt out and I don't know how to get it off. It's the drive belt pulley.

Hi,
By far the easiest method would be with air tools.
If not available, another method is hand tools and holding the flywheel by some method. By hand tools I mean something of significant size and weight because the bolts have significant torque applied in tightening them. (If all you have is pliers, an adjustable wrench, etc.; you will need assistance by someone more appropriately equipped!)
The flywheel must be held to apply force to loosen (or tighten) the bolt fastening the pulley. The housing(s) must be removed to expose it. Once exposed carefully raise the starter pinion to mesh with the ring gear on the flywheel; and, with a doubled over rag, wedge the two gears together by inserting the rag between the meshed teeth. Note: care must be taken as the pinion will try to be forced downward, so the wedging must be achieved with great care or it will come loose when trying to loosen the bolt on the pulley with skin-removing results to the hand(s) of the person loosening the bolt.
Peace,
Clarke