I’ve got some questions recently about updating the ADP1 (android dev phone) from one version of android to another. Recent version is 1.6.
Here’s a post I’ve used doing it successfully (and a bit easier than following the HTC developer guide): link.

Do not use Safari when downloading the packages from the htc-site (http://developer.htc.com/adp.html)! Safari by default decompresses the zip-files, which will be corrupted on the device.

Here’s an extract from the above link to the post;
1. Download the “Radio Image” file (ota-radio-2_22_19_26I.zip) and the “Recovery Image” file (signed-dream_devphone-ota-147201.zip).

2. Make sure that a MicroSD card is in the phone, and connect it to a computer via USB (non-Mac users may have to install certain USB
drivers first). Select the USB notification when it appears on the
phone, and when prompted, mount the device.

3. Copy the “Radio Image” file (ota-radio-2_22_19_26I.zip) to the root directory of the MicroSD card (I simply used Finder to do this) and
rename it to “update.zip”. When finished, unmount the USB device (I
used the “eject” button in Finder).

4. Turn off the phone (by holding the “end call” button). While
holding down the “home” button, turn the phone on again (again, by pressing the “end call” button). When you see the “!” icon, flip out
your keyboard and press the key combination ALT+l (that is a lower case “L”). When you see the console-based menu appear, press the key
combination ALT+s. When the progress bar completes, press both the “home” and “back” buttons on the phone at the same time. This reboots
the device, which should eventually bring up Android as normal.

5. Repeat step #2. Delete the “update.zip” file from the MicroSD card (I did this using Finder).

6. Copy the “Recovery Image” file (signed-dream_devphone-
ota-147201.zip) to the root directory of the MicroSD card (I simply
used Finder to do this) and rename it to “update.zip”. When finished, unmount the USB device (I used the “eject” button in Finder).

7. Repeat step #4. When finished (and after a long initial boot), you
should be running Android 1.5. You can choose to repeat step #5 to cleanup the unneeded file from the MicroSD card.