Dell Poweredge R510 - RAM upgrade

Hi

We have a Dell Poweredge R510 with a single Xeon processor and 12GB of RAM (3x4GB).  We wanted to double the RAM and were told by Dell that 3 more sticks of 4GB would work for us but I thought that you could only use the 4 slots that are associated with the single processor that's installed, is it right that we can just put 3 more sticks in and if so what slots should they go in?

Thanks in advance for your help.

Alan.