Capacidad de alumnos en Aulas

Para cada aula ustede puede especificar el número máximo de estudiantes que pueden acomodarse.:

Then for each class you can specify the number of it's students:

You can also specify the size of each group if you are using the groups:

Note: you do not need to specify this information. Specify it only for rooms where you are expecting the problems. Usually it is enough to specify the available classrooms for each lesson. See:
Asignar lecciones a aulas