Bios Mods -The Best BIOS Update and Modification Source

hello, my name is david I am french . I have a problem I have a dell optiplex 745 , I put 8 GB of RAM and I put a core 2 duo E7500 but he doesn't work on this motherboard, I searched and used lots of programs but none work for mod the bios.
anyone know it change a dell bios that is .exe ?

my bios is heiden2.6.6 on the dell site

thanks you for help me