Many mobile providers include a rather ugly and branded theme on your BlackBerry Z10 phone by default. To change the look of your phone with different backgrounds, fonts and colours, you can download bb themes from BlackBerry App World. Here is the tutorial about how to change themes On BlackBerry Z10 phone.
* From home screen, swipe down from the top of the screen.
* Tap Setting, and go to Display > Screen Display.
* Scroll down to the Theme section, and tap on theme. Highlight a different theme you would like to use, and tap it and then Activate. Now your Z10 are applied with a different theme you are happy with..