This article will help you locate and edit your custom spellingdictionary. The custom dictionary located in the following Windows directory for HelpStudio users:
For Document! X and Document! X & HelpStudio Bundle users, it is located here:
The items are stored as simple plain text words - with one word on each time. You just need to simply edit the file in a text editor (such as notepad) to change and/or remove items from the list.