I have a existing Hotel. Remodeling the bathrooms, all the wire is ungrounded romex. My question is..
Do I need to run a new 20 amp #12 wire to each bath for the gfi recep, or can I just replace the exsiting recep with a gfi recep?

The only person that can answer that will be the building department inspecting the job.

The NEC is not retroactive, if the circuit is in place when you get there you can continue to use it.

If it is a new circuit then it must meet the current NEC.

That said you may have local rules that require updating if the remodel is extensive.

For replacing outlets you might want to check 406.3(D)(2). As an inspector I would be more more interested in the GFI protection than putting them on 20 amp circuits.
Alan

Alan- you should expand your reference to include 406.3(D)(3)(b).