I have a Delta push down bathtub drain stop, but it is worn and does not stop the water. It does not unscrew as far as I can see how do I get it apart without removing the tube which I can not do?

There are two types of tub drain stoppers for the delta brand - lift & turn and toe tap.

Lift and Turn:
The lift & turn stopper for the bathtub unscrews counterclockwise while in the full up position.

Toe Tap:
The toe tap stopper does also but if the cap may unscrew from it before the entire stopper comes out. In that case, there is a nut that is now exposed and can be accessed to unscrew the assembly.

If either of these is "spinning" without unscrewing, the threads are stripped and you would need to exert upward pressure while unscrewing in hopes of uncoupling this from the bath waste. If that doesn't work you would have to unscrew the bath waste flange from the drain pipe.
This will require access under the tub. I hope this answer the question for you. Thank you for using FIXYA. Jeff

Thanks for all your help. That was so easy to fix. I just had to unscrew this counter-clockwise and the plastic looking metal cap popped off and then I needed a standard screw driver to unscrew it. Jeff you "ROCK"!
Todd