Need help with sidekick!?

Ok so i have the new sidekick that u can change the cover thing and im trying to change the theme in the back but i cant i want to add this pic from my computer and put in my sidekick as the theme. I've connected the usb cable to it but i dont know what to do know. so what do i do ...ohh and does anyone no how to add a ringtone to the sidekick without actually downloading it from the internet becauce i have none on my sidekickNeed help with sidekick!?sorry dont have one