How to edit security question?

[Abronsyth]

For some reason I cannot figure out how to change my security question for registration. It's not an option on the Basic Settings page via the ACP, and apparently I am unable to edit it in phpMyAdmin, as it says this;
"This table does not contain a unique column. Grid edit, checkbox, Edit, Copy and Delete features are not available."

Any ideas? I haven't edited this table at all, so I'm not 100% sure what's going on since I thought I used to be able to.