You should have custom recovery installed in your phone
To install custom recovery folllow this guide Installing Custom Recovery
Void rom Download links
Copy all the files from your SD Card to your Computer because we need to format and make partitions on SD card in order to install/flash void rom.
Boot into custom recovery mode and select Partition sdcard
Partition Items will be listed as shown below
Select Partition SD . It will ask for swap size and ext size.
Set the swap size to swap: 0 and ext to ext: 512
After partition is done, convert the partition to ext3 by selecting the SD:ext2 to ext3.
After that convert it again to ext 4 by selecting SD:ext3 to ext4.
Go back to the main menu and select wipe.
Wipe the following
– Wipe data/factory reset
– Wipe cache
– Wipe Dalvik-cache
– Wipe SD:ext partition
– Wipe .android_secure
Go back to the main menu and select USB-MS toggle. Connect your phone to PC/Computer using USB cable. If your phone is not detected, you have not installed the drivers. Download and install Lg optimus one USB Drivers on your computer.
Copy the downloaded zip you wish to flash into the root of your SDcard; unplug afterwards.
In the main menu select flash zip from sdcard and select the zip file you just copied.
After the installation is completed. Reboot phone. Thats it.