From the screen shot it looks like you have SEPM and Luadmin on the same server, Symantec does not recommened these two on the same server.
LiveUpdate Administrator 2.x and Symantec Endpoint Protection Manager on the same computer
http://www.symantec.com/business/support/index?page=content&id=TECH105076
Screen 1: TempDownload is where Luadmin stores all the downloaded contents. wrt to Luadmin I dont suggest to delete anything...from here
From Screen shot 2.
Content\Alphanueric folders are where the Virus Definitions for SEP 12.1 32bit and 64bit clients are stored
Each of the subfolders in these folders will be one specific virus definition revision. As for the sizing for each revision SEPM stores full.zip file (around 200-250MB) and extracted "Full" folder (around 450MB) - altogether one revision takes then around 650-700MB + additional space if there are any delta definitions files inside (.dax) - this needs to be mupltiplied by factor of 2x - as per 32bit and 64bit definitions stored.
As you are keeping 20 revisions - 1.3/1.4GB x 20 = the content folders for the AV defs only may increase in size up to 26 GB / 28 GB and this is expected.
if you want to minimize you can set the number of content revisions under SEPM- Admin -Severs tab.
Make it 3