-go to your main page
-click settings (its right next to wallet)
you will see

'Public Profile Settings'
PROFILE PICTURE URL
COVER IMAGE URL

in PROFILE PICTURE URL you will put in the url of the profile pic u want

COVER IMAGE URL is the url of what the banner/cover picture will be

you will NEED the url of the image you want to use
to get a url you can use sites like tiny pic