Within the Applications Settings: Dropdowns tab, you can set up Value Lists. These lists control the options that are available in the Memos, Condition Type, Document Type, and Reject Reason drop-down menus.
To add additional options to these drop-down menus, simply find the correct value list, i.e. Condition Types. Click "Add a value", and write the value in the Text box.
Some Dropdown Types can have Sub-options. These are added in the Sub-options area, one per new line.