You can change your profile picture easily under "profile" once you are logged in.
You can change your album cover after you uploaded the photo you want to use.
After you login you will see a little gear avatar right in top at the right of your album cover (standard the album cover is trees).
Click on this little gear and then click on "modify cover".
You have now the choice to use a photo that you already uploaded or you can upload a new photo and use it for your cover (that's the the large picture that will be shown in top of your page).