Hi,
Each project’s LOC is the number of lines of code found in the most recent analysis. Take the LOC from largest branch (assuming at least Developer Edition) from each project, and add them all together and that’s your server LOC. This is not about the total number of lines you’ve ever analyzed, just what you’ve got under analysis now. So if you drop files from a project (and re-analyze) or delete a project altogether, your LOC goes down.
Regardless of your LOC, Community is free. You just won’t get the coolest features. 
HTH,
Ann