Slowly, over several years or quickly with high body count and/or slim odds of lasting success depending on the nature of the proposed changes.
History is littered with attempts to move fast and break things but lasting change takes time because people's attitudes have to change. At the end of the day even unpopular dictators require some amount of consent of the governed in order to rule. You can try to play politics and then use the power gained to push whatever it faster with propaganda, indoctrination, legislation (which is somewhere between an appeal to authority and coercion when used in this manner) but if you push faster than the population actually wants they might push back.