*I just did this a second time on my wife's phone and was successful again! Here is the edited step-by-step instruction guide.
Download link:
http://bit.ly/cCiIQu
1. Turn your phone off
2. While holding volume up, press power
3. At the prompt, choose bootloader
4. At the next prompt, choose recovery
5. You will eventually get to a black screen with a phone and triangle
6. Press power and volume up at the same time
7. Some blue writing will appear at the top of the screen. Select "Apply update. zip" (I renamed mine "update" without the quotation marks)
8. Yellow typed info will scroll on the screen. Once the update has finished it will tell you, "Reboot to finish installation."
9. Select the proper instructions for the reboot and use the power key to enter, as instructed. A weird phone with an arrow will show up and turn on and off a few times. WAIT for this to finish. It acts like your phone bricked, but it will eventually boot up correctly.
10. Once the phone boots, it will go through 2 more update screens. The last one takes the longest - about 5 minutes.
Your Evo will reboot and that's IT!!
*This is assuming you already copied it to your SD card