Currently, Starter and Lite plan users may add up to 5 images on their photo gallery.
If you wish to add more, then the Basic, Plus, and Reputation plans offer unlimited photo additions. To upgrade, just access the Upgrade tab on your Business Hub here.
UENI recommends the following resolutions:
Logo, minimum size 200x200px
Header image (big banner image at the top of your website), minimum size 1900x500px
Gallery images, minimum size 1024x300px
If you're using a Windows operating system, use this third-party tool to resize your images.