If you are currently paying a DVR fee (SD or HD DVR that requires one), you can switch to DVR Advantage. I do not know if the 5$ upgrade/change rule applies, or if there are contractual requirements. As far as I know, unless you use Dishin-It-Up, you will not be put into a contract to change to DVR Advantage.
You should ask to make sure, but I believe this to be how it works. Your first DVR would be covered (without fees).
It has nothing to do with your time you've been a customer. New customers can get DVR Advantage too.