The DMR upgrade came out only about 6 weeks ago. It's likely that your unit was assembled before that release. The firmware version that enables DMR is 1.07.06. To check what version you have:
Scroll down to Settings & hit 'E' (yes)
Select See Scanner Info & press E again
Then select Firmware Version & press E once more to verify what is in the scanner. Note that if you see "Upgrade" on the initial menu, right above the See Scanner info, then you likely have the correct firmware.