In order to undergo the Angel Ritual, you must first be an Earthling yourself, and have an Angel willing to help you through your transformation. Most angels would send you on a quest to go get the blood of a demon, or some other kind of test.
The Actual ProcessEdit
It doesn't matter. Really, it doesn't. Most Angels will just baptize you and bingbaddaboom, you're an Angel. Angels can add their own flair to it as well. So, go nuts.