To change the bullet type

To change the bullet type

When I want to change the bullet type in my text, I click the arrow by the bullet button, then a box would show to contain the lists of bullets to be selected. But I found the box was behind my slide. A large part of the box was blocked by the slide. Therefore, I could not change the bullet any more. What's wrong with this and how can I do with it?

Thank you very much!
isami.chwang