You can right click on the graph, select Properties, then change the Y Axis Range.
However, I believe this is limited to 2^31 as the highest value it will accept, if you enter something higher, the results will not be as expected. Not sure if that's only if you're using 32bit Java and Console. Haven't checked with the web interface.
Alternatively you can simply zoom in on the part you want to see in detail (I think that only works in the console, not the web interface).
Hope that helps