how do i access the display settings?

i found this in the readme:

    Using the Display fields settings each field of a simplenews newsletter can
    be displayed or hidden in plain text and/or HTML newsletters. You find 
    these settings at: 
    admin/content/node-type/my-node-type/display

i can't seem to find/access that URL regardless of what i put in for "my-node-type." am i missing something? it hiding/showing certain fields sounds very useful and i'd love to use it.

thanks!
debra