Adding extra ram

Hi guys,
I bought a computer system from 'Overclockers' about 3 years ago and it came with 8GB of 'Hyper x' ram.
Im now thinking of adding another 8GB of ram and not sure which product to buy. ive attached a picture
of what I have in the computer at the moment. could you advise me what would work best with what I have
at the moment.

Many Thanks
Jm

That's a 2 x 4g kit correct? Do you really need more then 8 gigs of ram? If you do then buying a matching set is your best bet.