If it's the same consultant just tell her you will be going to the different group just so she knows. If it is a different group, again I would just tell your current consultant that you need to change groups - you don't need to explain why unless you want to and then just turn up at the new one. You shouldn't need to pay extra just your regular class fees.
i just recently swapped, i informed my old consultant and then just went along to the new one. filled in a form and carried on from there no extra fees (unless you missed the week before and didnt let them know)