The vga BIOS just tells the VGA what clock speeds and voltages to use. you cant enter the VGA BIOS like you can the motherboard BIOS. From within windows you can flash the VGA bios with a newer one or overclock it but i only recommend this only if you already know what your doing
You'll need to download the bios from your cards maker, put it on a floppy disc, and then resart your computer with the floppy inside. You should be prompted about installtion....I think :