Thanks shawno but I'm still quite confused.
I don't understand where I should be looking for the usergroup settings. I thought that I should go to, say:
ACP -> Usergroups -> Usergroup Manager -> Administrators (Edit Usergroup, click Go)
and then find a group of settings for iTrader on that page (presumably near the bottom). After making the settings for that usergroup I would then proceed to repeat the process for each of my other usergroups.
Am I looking in the wrong place?