1: press and hold on the homescreen.
To the right there you can see theme's and select others.
2: under settings - display.
Scroll to the bottom and you will see the option for setting themes.
3: sometimes when you download a theme it will will leave a quick setup between the rest of your apps.
Next time please see the manual that came with your phone.
Sent from my LT30p using xda app-developers app