New Rack Server

Hello,

We have a PowerEdge R520 Server and now it's about time, that we upgrade. As i wasn't here when it was bought and installed, I don't know the exact specifications. Is there a way, I can compare the Specifications from the PowerEdge R520 with the new ones, so I can imagine, which one to buy to upgrade the R520? I can't find any details on the R520.

Also, is there like a successor of the R520?