As far as I know, you cannot change it. You can, however, use a different banner (service) to customize it to your liking.
If you just search up Minecraft banners, there's quite a few services that can help you create banners. You can also create your own with programs like Photoshop or paint.net, just make it the same dimensions as you want. These, however, do not include the player stats. If you want a custom banner that also shows server information, it's a bit more complicated.
Also having trouble with enabling query. It was set to false in the configs so I set to true. Do I need to upercase the T because in the rest of the config file true is true not True and false is false not False
There's not really any point in doing so, just upload the image to wherever you want, or host it with an image hosting service like imgur. No, I don't think it is case sensitive. You can check in your console when you start your server up to see if Query has been enabled or not or try querying it.
If you add your server to minecraft-mp.com, they'll provide you with a number of banners that you can use. For example: http://minecraft-mp.com/server/45326/banners/
