Add, change, or delete a word in the custom dictionary
1. On the Home screen or in a folder, click the Options icon.
2. Click Typing and Input > Custom Dictionary.
• To add a word to the custom dictionary, press the BB (Menu) key Select New. Type a word or letter combination. Press the Enter key on the keyboard.
• To change a word in the custom dictionary, press the BB (Menu) key Select New. Change the word. Press the Enter key on the keyboard.
• To delete a word from the custom dictionary, highlight the word. Press the BB (Menu) key Select Delete.

Source : http://btsc.webapps.blackberry.com/b...ListHelperImpl

Typing>Custom (Bottom of the page)