Go to the "section expert" found under "report" in the menu. Here, click on the section you need to supress and tick the "suppress if empty" checkbox.
They may actually be called differently, I'm translating from a Dutch version of CR. Anyway, I think you'll find it :)
<Edit:>
I think this is only true if you're actually designing in Crystal Reports. Not sure for Visual Studio...
</Edit>
You could also check these links if my suggestion doesn't work, or you want to suppress based on some condition:
Suppress blank section of data field and the label[
^]
Crystal Reports XI, how to suppress blank row(s) in detail section of the report?[
^]
Good luck!