To block another user simply click the settings icon found on each profile and choose block member. You can block someone to prevent them from seeing things that is posted on your profile, starting conversations with you or adding you as a friend. Blocking someone you are friends with will automatically unfriend them.
Hover over the banner image till the Change cover icon appears. Select Upload new. A window will popup for you to select an image from your device.
If you need to adjust the position select Reposition. Click/press the banned image and while continuing to press you can move the image in any direction as long as the image size is bigger than the box.