Having trouble changing from ram single channel to dual channel. Please help if possible.

Okay so I purchased additional ram today (corsair vengeance 1 x8gb DDR3) and have placed it in my computer however I cannot figure out how to change to dual channel.

I have an ASUS Z87 sabertooth motherboard and have checked my BIOS settings but I cant find where I can switch to dual channel. I ran CPU Z and it states that I am on single channel. https://gyazo.com/312843628b054df6b9b2fd9bcde0f148

Has anyone any idea how I can swap to dual channel so I can get both my old stick of ram (8gb) and my corsair vengeance ram working.

Thanks.