The Johari Window originated in a 1955 paper by Joseph Luft and Harrington Ingham, "The Johari window, a graphic model of interpersonal awareness". There's more information about the Johari Window on its Wikipedia page, including some context.
This variant was invented by Kevan Davis, the creator of this site, and uses rough opposites of each of the Johari Window's fifty-five adjectives.
You can't. Because we didn't mess you around with passwords and logins when you signed up for your window, there's no real way to verify who's doing the editing or deleting. If you want to start again with different adjectives, just set up a new window with a new name. If you don't want people to see your Johari window, just don't link to it.
It's http://kevan.org/johari?view=username, where "username" is the name you signed up with.
The URL to pass on to your friends is http://kevan.org/jh/username.
You can't yet, although there may eventually be a feature for you to replot your window with selected votes ignored.
These implementations follow Luft and Ingham's original framework, specifically that "five or six" words be chosen. Although these are arbitrary numbers, having some sort of minimum and maximum means that participants are forced to consider and compare the adjectives carefully, rather than sweepingly ticking all that apply and obscuring the most important adjectives, or holding back on what could otherwise be an insightful set of attributes.