1- Login on the character you want to leave the guild with.
2- Press Alt-G (or Ctrl-G?) to bring up the Guild information screen.
3- Go to the second tab from the left and scroll down the list until you find your name.
4- Right click on your name and select Leave Guild from the list of options that pops up.
5- Enter a reason for leaving
6- Press OK
7-
8- Profit!!
