How to change memory multip in biostar x58A

Sup guys,
im buying 6gb of gskill trident 2000mhz cas8 or perfect storm 2133 cas 9 (wich one would be best? not thinking about the cash etc...).My mobo is a biostar tpower x58A, and im looking for to overclock my i7 to 4ghz or 4.2 ghz. The problem is that I dont find anywhere the memo multiplier. I need to change it to 2:10 to get 2000mhz at 4.0ghz isnt it?
Where do I change the multiplier?