LOL this thread is way longer than it needs to be, ezflash is an ASUS thing so your board doesnt have it, it comes with Q-Flash instead.
1: format the whole USB stick as FAT32 dont waorry about whats already on there, this is bundled stuff (bloatware)
2: download the bios file you want to flash
3: extract the downloaded zip file to somewhere easy like the desktop, you'll see 3 files.
4: just copy the bios file only to the USB stick, drag and drop, copy and paste, anyway you like, just make sure it goes on the stick. you dont need the autoexec.bat or the Efiflash.exe file, just the bios file.
5: leave usb stick in the computer and reboot and enter the bios
6: select Q-Flash option in the bios, it will scan for drives, see your USB stick and ask you to select the file you want to flash.
7: select it and begin the flash, takes a few mins.
WARNING: Do not remove the USB Stick until after the computer restarts.
I cant make this any easier.
Bioses for your board for Rev 1.0 are here:
http://uk.gigabyte.com/Motherboard/GA-Z77M-D3H-rev-10#support-dl
Bioses for your board if you have Rev 1.1 are here:
http://uk.gigabyte.com/Motherboard/GA-Z77M-D3H-rev-11#support-dl
Make sure you select the correct revision, your revision of board will be written on the front of the board somewhere or on the box the board came in, see picture:
http://i66.tinypic.com/fxcu9c.jpg