[REQUEST]Help unlock VGA settings in Lenovo B450 bios

[dayz]

Hello, im new with this forum. My laptop is Lenovo B450 and i spend many time in the internet to find a way to change my vram amount. My vga card is NVIDIA G105m and in the NVIDIA official site the max amount of its vram is 512 mb but my laptop only shows 256 mb. Well my spec are

Windows 7 32 bit
Nvidia g105m 256 mb
4 gb ram
Intel pentium dual core T4300

I didnt find any vga settings in the BIOS. So can someone help me to unlock the VGA setting in my bios. you can download it here
http://consumersupport.lenovo.com/ot/en/..._2109.html