Since I made an update of my Alienware BIOS (A10 to A12)  the usable ram drop to 7.17gb instead of 8gb, I would like to go back to A10, but how?  i tried with ''Alienware_X51_R2_A10.exe'' but it doesn't work.(the RAM is detected when I look in the BIOS and windows10)

My pc is a Alienware x51 R2

Thank you and sorry for my terrible english!