An individual's view changes from being interpersonal racism to institutional racism when he or she begins expressing racism in institutional practices; this includes expressing racism in social groups that support or enforce racism.
Interpersonal racism, which is basically racist actions fueled by stereotypes and racist tropes, is enforced by institutional racism. An example of Institutional racism is governmental policies and rules that reflect a negative attitude towards a race; this includes things such as the Jim Crow laws which segregated African Americans and White people.
I'm not too knowledgeable on this subject, but I hope this helps! :)