Are there links to the recommended banner sizes?
I had answered your ticket, hope you got that
Here are tutorials as I'm not sure which one you are needing:
https://community.socialengine.com/blogs/597/72/elpis-theme
https://community.socialengine.com/blogs/597/67/banner-manager
Due to the responsive themes, banners might need resizing based on what content is in them.