In the effort for a president to stop or reduce corruption in any nation, the said president has to be discipline and really prepared to stop it, because there will be a lot of other people trying to frustrate his effort.
It's not easy to end corruption in a system that is really affected, but if you are determined as the president and also disciplined,  you can really try to reduce it, even if you can end it completely, because I believe that corruption can not be stopped,  but you can reduce it, by putting policies in place that does not favor those that are corrupte.