There are essentially two ways to hold the tub spout: threaded, or push on. If it is push on, then there will be a setscrew accessable from somewhere on the bottom. It might be recessed, and seeing it can be a pain. A mirror might help along with a bright light.
Keep in mind that if they used silicon to seal it to the surround, that acts like a VERY strong glue, and you have to break that seal first regardless of how it is attached.