MS Bookings - How to increase number of participants for an existing group meeting

I hope someone has an answer ...

My service has a group booking with 12 participants. Due to a high number of interest I would like to increase the number to 16.

It seems that it is not possible in the existing service as an increasing of the number dublicates my service with the higher number. If I would publish the service I have 2 services one with 12 participants and one with 16 - this is not what is required.