Octavian, who came to be known as Augustus, did not want people in Rome to think that he was changing the political system in a radical way. He had seen what had happened to his adopted father, Julius Caesar, when he had tried to affect radical change. Therefore, Octavian tried to be much more subtle.
The main thing that he did was to keep the Senate in a position of official power. He proclaimed that the republic had been restored and maintained the Senate's official power to make all the laws. Octavian did take a tremendous amount of power for himself, but he did so in ways that did not seem radical. He had himself named to established offices, having the Senate make him a consul and later a tribune. This meant that he could have the appearance of simply going back to the old ways even though he had all of the real power.
Octavian, then, kept political institutions the same as they had been in the sense that he gave the old republican institutions official power even though he was really changing the workings of the system.