How to install a themes for my motorola L7

To instal themes first you have you have to download and install skinmanager you can search in www.google.com then connect your phone to the computer via usb cord make sure you have selected the data and fax connection fron the connectivity the you will be asked to instal your phone then select it to chose manually and direct it to the drivers folder in skin manager once done another 3 or 4 same messages will come do the same then run skin manager then add your desired skins.

Need a bit more info. Where is the "skin" you are wanting to use? Is it a photo on the phone or a pic on a PC?

If it is a picture currently on phone just go Menu->Multimedia->Pictures->Scroll to pic you want to use->Press left softkey(OPTIONS)->APPLY AS->WALLPAPER.

If this is not what youre talking about let me know.
Good luck.