The energy levels of holes in a p-type delta-doped GaAs structure under a magnetic field are theoretically calculated within the framework of the effective mass approximation for a uniform acceptor distribution. The electronic structure is calculated by solving the Schrodinger and Poisson equations self-consistently. The effect of the magnetic field on the potential profile changes the degree of the confinement and localization, and thus this behavior can be used to study these systems in regions of interest, without the need to grow many different samples. It is found that the heavy-hole subbands contain many more energy states than the light-hole ones; the population of the heavy-hole levels represents approximately 91% of all the carriers without magnetic field. With increasing magnetic field the total population of the heavy-holes increases and the number of filled states changes.