Yeah you need to delete the port from the gateway and re-add it to change it. You will need to remove route pattern/route group dependencies in order to delete the port. I recommend you use the Dependency Records to find out what RGs this port is assigned to so that you can add it back in.
If these are FXS ports, I'd actually recommend you keep it at POTS until CM 8.5, though, since LS is the default configuration for the port in IOS, and there is this bug on CM, which isn't fixed until 8.5:
CSCtf22348
MGCP FXS GroundStart and LoopStart need Prefix DN; remove Attendant DN