I think the tub is leaking from the drain and waters leaking downstairs I want to replace the rubber o ring seal in the drain

How do I take the drain off to replace the rubber o ring seal?

HI Sara...

Tub drains don't usually have ORING seals... not usually.

What kind of tub drain do you have.. a trip lever type or a toe touch type?

Also, what makes you suspect the tub waste and not the tub/shower valve?

What steps have you taken to isolate the leak?

Please answer all questions...

Mark