Head to Admin > Games > Games, then click [Servers] and make sure you have the right server selected.
Then head to Admin > Characters and Accounts > Rosters, then change the server and guild name of the roster of your site.
Did both of these and I'm still getting my old guild from another server. Any suggestions how to fix that?
Edit: Figured it out. Had to delete and remake this roster. Apparently doing this points it in a new direction.
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I don't worship the devil, but I do agree with a lot of the things he tells me.