A Bipolar 1 has had at least one extreme episode, I believe a bipolar 2 goes up and down with hypomania but has not experienced an extreme state (psychotic or delusional episode).

Bipolar 1 shall we say is shifted higher - extreme episodes and some depression
Bipolar 2 is shifted lower - experiences frequent hypomanic states and extreme depression

Types of Bipolar Disorder: 1, 2, Mixed, Cyclothymic, and More