How to unplug bathtub

Need more information. Is the drain a lever type or different? How old is it?

If this is a average bathtub it has a chorme overflow plate/trip lever under the spout. Remove the two screws on the plate with the lever. Pull out and up to get the plug and linkage out. Then run your snake down the open hole. You will hit the bottom of the trap about 18" in and come up against some resistance, work it on past. The tub drain pipe shouldn't be too long,8 to 12 feet so you shoudn't have to run out too much snake to reach the clog.
After you have opened up the drain line fill the tub with hot water to flush out the line. Good luck, Tom