When you click on the notifications but marg, there should be a section at the bottom that enables you to manage them.
I'm on my iPad right now so my notification bit doesn't work, but I'm pretty sure once you click on the bottom the manage them, you can also delete them all, and then change your preferences if you want for future.
Alternatively there is a little arrow next to the notifications (an up arrow), if you click on that it will hide the whole notification bar.. You just need to click the down arrow to bring it back.
Hopefully that helps.
