wordplay

I'm currently using Avtech AVC798BD with avtech KPC139E camera . I'm not satisfy with the resolution image of the KPC139E camera.KPC139E camera resolution is 520 TVline. I'm planing to upgrade the dvr brand that support D1 recording. If i upgrade to D1 supporting dvr, will get any image resolution improvement ? One more thing is, the Avtech AVC798BD dvr why did not support 2 or 3 month even play back? I'm using 2 TB HDD for that dvr. How to view 2 or 3 month even that stored at that HDD?