Open the theme in your browser and read the notes in the code- they make it easy to customize what you want! Official topic with visual help: http://myanimelist.net/forum/?topicid=1380020

More backgrounds can be found here: http://imgur.com/a/P9BFr
More renders (characters) can be found here, without watermarks: http://imgur.com/a/ydViG
You can paste the URLs from the albums in "Provide your own" on this theme's page,
or download the images and use them for "Upload your own".

If you're having problems or don't know how to use CSS, try my Easy themes as an alternative to this one. These themes are much more simple and direct to use and let you customize the same parts individually. Keep in mind these styles OVERWRITE the theme on the CSS editor!

My Easy themes, combine all three!
For banners: http://freestyler.ws/style/119620/myanimelist-customize-your-banner-easily
For backgrounds: http://freestyler.ws/style/119619/myanimelist-add-custom-background-images-or-color
For side characters (renders): http://freestyler.ws/style/128636/myanimelist-add-custom-characters-on-the-sides

Others:
http://freestyler.ws/style/119660/myanimelist-re-color-the-bubble
http://freestyler.ws/style/119572/myanimelist-restore-profile-button
http://freestyler.ws/style/128632/myanimelist-revert-or-edit-my-page-text
http://freestyler.ws/style/119617/myanimelist-remove-new-links
http://freestyler.ws/style/119570/myanimelist-remove-blue-footer-social-media