Before I start this, just a word. If you do these steps, you will reset the router to factory settings so if you had some sort of special set ups, you might or will lose them. You will have to set them up again.
And since you asked this months ago, not sure if this is pending
I have two DI-624's and the only way I know to do this is to hold the reset button (located next to the power cord plug in the back of the router) for at least 10 seconds. Once you release the reset button, if you look at the front panel lights, they will flash and then the router will go through the boot up process. After about 30 seconds, your password will be reset to "blank". Just type admin and leave the password blank.
In the future, what I did to remember this (in this world of having to remember everything) I drew out a plan. Just a rough picture of the router, under that I wrote down the log in name, below that the password, below that I listed all the special settings I made to the router including the SSID. That way if something like this occurred, I have my handy dandy cheat sheet.
I hope this helps.
