( If you only have one BIOS chip on your card, flash the only BIOS at your own risk )
Usually You have two BIOS positions on your card: (switch)
#1: Unlock BIOS (You can flash this one)
#2: Lock BIOS (This is the default BIOS you can't flash)
It is important to save the BIOS #1 even if you have two BIOSes (BIOS can have different clock state)
Now first step is to download ATIwinflash
Then extract it on your Computer and insert the BIOS you want to use in that folder like this : (In this Case, the wanted BIOS is 7970XFX.rom ) (Bios collection Link at the end of the post)
It is also important to take note of the LOCATION of ATIwinflash.exe for further use

Now go in start menu and write cmd.exe in search and open command prompt (cmd.exe) with right-click and "Run as Administrator
Once open, write the location of ATIwinflash with CD before the command (Since ATIWinflash is on my D:, I need to write D: then enter first, as shown here)

Then enter will give you this window

Now, write this command : atiwinflash -f -p 0 "NAME of the BIOS".rom then enter. In my case its atiwinflash -f -p 0 7970XFX.rom

Then enter and the Flash Will proceed

When complete it will show a windows like this one and will ask you to reboot. (Do it unless you have more than one card to flash)

Crossfire Cards
So the "0" in "Atiwinflash -f -p 0 7970XFX.rom " meant the first Card
0 : First PCIe Slot
1: Second PCIe Slot
2: Third PCIe Slot
3: Forth PCIe Slot
So if you have 4 Cards you will have to enter those commands (No need to reboot between each flash, but very important to reboot at the end of the last flashed card)
atiwinflash -f -p 0 7970XFX.rom
atiwinflash -f -p 1 7970XFX.rom
atiwinflash -f -p 2 7970XFX.rom
atiwinflash -f -p 3 7970XFX.rom

DONE
GPU BIOS Collection
ATI has 3,595 different BIOSes
Nvidia has 4,185 different BIOses
Usually You have two BIOS positions on your card: (switch)
#1: Unlock BIOS (You can flash this one)
#2: Lock BIOS (This is the default BIOS you can't flash)
It is important to save the BIOS #1 even if you have two BIOSes (BIOS can have different clock state)
Now first step is to download ATIwinflash
Then extract it on your Computer and insert the BIOS you want to use in that folder like this : (In this Case, the wanted BIOS is 7970XFX.rom ) (Bios collection Link at the end of the post)
It is also important to take note of the LOCATION of ATIwinflash.exe for further use
Now go in start menu and write cmd.exe in search and open command prompt (cmd.exe) with right-click and "Run as Administrator
Once open, write the location of ATIwinflash with CD before the command (Since ATIWinflash is on my D:, I need to write D: then enter first, as shown here)
Then enter will give you this window
Now, write this command : atiwinflash -f -p 0 "NAME of the BIOS".rom then enter. In my case its atiwinflash -f -p 0 7970XFX.rom
Then enter and the Flash Will proceed
When complete it will show a windows like this one and will ask you to reboot. (Do it unless you have more than one card to flash)
Crossfire Cards

So the "0" in "Atiwinflash -f -p 0 7970XFX.rom " meant the first Card
0 : First PCIe Slot
1: Second PCIe Slot
2: Third PCIe Slot
3: Forth PCIe Slot
So if you have 4 Cards you will have to enter those commands (No need to reboot between each flash, but very important to reboot at the end of the last flashed card)
atiwinflash -f -p 0 7970XFX.rom
atiwinflash -f -p 1 7970XFX.rom
atiwinflash -f -p 2 7970XFX.rom
atiwinflash -f -p 3 7970XFX.rom
DONE
GPU BIOS Collection
ATI has 3,595 different BIOSes
Nvidia has 4,185 different BIOses