I'm sure you've noticed by now that Apple is not really into personalization of their iOS devices, offering little in the way of customization, especially compared to other portable devices. You can only change the wallpaper on two screens, can't change icons, etc. Fortunately for me that is not a big deal as I didn't even engage in such things even when I could on other electronics, but I know this does vex some people.
You can change themes, etc. On your iPad but in order to do so you will have to jailbreak it. We can't discuss that here at a corporate Apple website and can't provide links, but if you do a Google search for "jailbreak iPad" you'll find all sorts of information. Just remember that jail breaking your iPad voids your warranty and you won't be able to get any help here with any problems that ensue.