Best Performance for Memory Upgrade R610

I have an R610 with 6 @ Samsung 2GB modules for a total of 12GB RAM.

I need the RAM to be >= 32GB minimum and >= 48GB ideal.

I've read this memory doc a couple times but it's not straight forward enough for me. :(

http://www.dell.com/downloads/global/products/pedge/en/server-pedge-installing-upgrading-memory-11g.pdf

What do I need to do to get the best performance?  Toss the existing RAM and replace it all or simply add more RAM?

The modules are:

Samsung 2GB PC3-10600 DDR3-1333MHz ECC Registered CL9 240-Pin DIMM Dual Rank Memory