It's in the manual (page 50, 9-12) and also on AOR's website. Download and unzip the latest update, transfer the .dv1 to a clean SD card (your computer will need an SD card slot to do this). With the power off, insert the card into the slot on the DV1.
Now power up, and after the radio has started up, press F followed by 7. This is the configuration menu.
Use the 'down' key to find SYS UPDATE in the menu and press ENTER.
The firmware file(s) on the SD card will be shown. Use the UP or DOWN key to highlight the one you want and hit ENTER. The update process will begin. It will take a few minutes to complete and the receiver will re-start.
Some instructions I have seen tell you to remove power for a few seconds and then plug back in. I'm not sure you have to do this any more.
It sounds a long-winded process, but it takes just a couple of minutes and seems to work without any hangups. I've just installed 1702b in mine.
But of course you do need to be able to write to an SD card. Most PC's and laptops have them these days, but some don't.
Eddy - once you have unzipped the files (the dv1 file should end up about 720k), put your clean SD card into the card slot on your PC and just drag the dv1 file across to the card and drop it in. Then you put the card into the radio. Even I can do it, and that's saying something.