Disclaimer - Try this at your own risk. I'm not liable if you brick your phone. I didn't really know what I was doing, and probably shouldn't have tried it on my eris because I sold it on ebay a few days ago and i'm waiting for the buyer to pay me for it.. lol! This is a simliar process for installing updates on the Moto Droid.
NOTE: I DIDN'T LOSE ANY DATA AFTER THE UPGRADE!!
Okay, this is all coming from 1.5.
First, download this OTA file:
http://android.clients.google.com/p...36.605.1_1.17.605.1_release_0420.79112f65.zip
I named mine update.zip and put it on the SD card.
DO NOT name it PB00IMG.zip as it will try to load in the next step.
Turn off the phone, hold down VOL DOWN and POWER, just like you normally would to install a leak.
It will search for the files like PB00IMG.zip, etc..etc..
Scroll down to RECOVERY and press the POWER button. The phone will reboot with an exclamation point.
Press the POWER button and VOLUME UP at the same time, and you should be presented with a menu. One of the options should be "Apply sdcard:update.zip". Choose that one.
It will start the installation process.
I got a little worried because it started deleting files and stayed in one spot for what seemed like 10 minutes, (probably 4 in reality), but it eventually finished.
When it's done, choose the reboot option and let it do its thing. It will take a few minutes to boot up intially.