qnap memory upgrade

Hi I just got a TS-451+ and it came with 2GB of memory. I went to the local Transcend shop and I can replicate the same stick to have 2x2GB RAM in the unit. I'm now in a quandry. Can I install only 2x2GB, rather than 2x4GB as blessed by QNAP? I can't find anyone stating if this is OK. I saw one...