Four to five years is a long time and if serious enough, a head of state should be able to handle and reduce the number of corruption cases. Because it does not work alone, the government has many components that can be invited to work together to resolve this. In fact, if a head of state serves more than one term, it is very feared that a dynasty will be created, collusion that makes it easier for them to commit corruption. and if so, what does democracy mean.
It is not easy for any new president to stop the corruption. Even if the president has the intention to reduce corruption, it is not a one man show. This intent should be trickled down from the top to the bottom. But usually, the department heads and other politicians have the habit of making money through bribery and corruption, and they typically do not cooperate with the president's good intentions.
One may analyze the history of the most corrupt nations in the world, like South Sudan, Somalia, Myanmar, and other countries, and see why these countries have corrupt rulers, and new rulers also cannot bring about any changes.