First, you need hack your phone before install new theme.
Steps 1: download this file: http://hotfile.com/dl/43981093/add0199/AQA_files.rar.html
Steps 2: extract file "AQA_files.rar" to your Desktop
Steps 3: Run & Install "Flash USB Setup.exe"
Steps 4: Run & Install "WinImage Setup.exe"
Steps 5: copy file "KP500.flb" to C:\
Steps 6: go folder 'LG-Utils-EN" and run "KP500-Utils-EN.exe"
Steps 7: choose D, type "\\.\USB1" press Enter and them type "C:/KP500.flb" press Enter, type "CUST_THEME" press Enter
Connect as fast as you can your phone to your PC via USB cable (unplug the SIM Card, Memory Card and Batteries)
Wait the process....about 10 minutes. When finished, you will see twos files: .big file (about 1GB) and CUST_THEME file with no extension. You need copy and save file CUST_THEME in the safe place for backup.
Steps 8: Use winimage to CUST_THEME above you will see "Igapp" click on it to open, find folder "dmf". Copy all theme you have downloaded to this folder by drag & drop it.
Steps 9: Choose save from winimage menu and copy the CUST_THEME file you created to C:\
Steps 10: Unplug your phone from your PC
Steps 11: Run "KP500-Utils-EN.exe"
Type "C" press Enter
Type "\\.\USB1" press Enter
Type "C:/KP500.flb" Enter
Type "C:/CUST_THEME" Enter
Connect your phone to your PC as fast as you can and wait until the process completed
Insert SIM Card, Memory Card, Batteries again and enjoy your new theme
Find more theme HERE