I want to update the tub drain with new style "step on" seal. How can I remove (unscrew) the old drain since there is nothing to grab on to turn it .

You would have to cut it out with a saw saw and fine tooth blade,put it in the drain hole and cut the side but be careful not cut the bath tub.I would highly recommend a lift and turn drain over a toe touch drain.

Abner, you are new and I don't want to be the guy who gives you your first red reputation point. This answer is totally incorrect. The tub drain can be removed/unscrewed with atub drain removal wrench, about $13 at Home Depot. It has four splins that fit into the four openings in the tub drain.

Thanks for your info but the drain had been in for 36 years and would only move with much help from a chisel and a big hammer.

Thanks for your info but the drain had been in for 36 years and would only move with much help from a chisel and a big hammer.
Did the old drain come out and did a new one get installed OK or is there still a problem?

Yes, the chisel and hammer method got the old drain out and the new one went in without a problem - after much WD40 and steelwool cleanup.

Many thanks for the help.