Transformation of the orientational structure in a plane-parallel cell of a cholesteric liquid crystal, was studied depending on the magnitude of the voltage applied to the boundary planes of the cell. The equilibrium configuration of the liquid crystal director field was found minimizing the free energy both analitically and numerically. We took into account the orientational elastic energy in the volume and at the cell boundaries, the energy of an inhomogeneous electric field, and the flexoelectric effect. Systems with large flexoelectric coefficient were studied in detail. It was found, that when small voltages are applied to the cell boundaries, a continuous Fredericks transition occurs first, and then, when certain characteristic voltage is achieved, a significant jump-like change in the orientational structure takes place, and this structure gradually changes with the further voltage increase. It is shown that various scenarios of transformation of the orientational structure can be implemented depending on the actual values of the set of material parameters of the system studied. The discovered ability to control the structure of a liquid crystal in a cell can find use in various technical devices.