I'm using a navigation bar on my website --deaconworld.net -- using the forum titles.

When being used as the forum titles [i.e.; 'Contemporary Issues'] there isn't room for all the forums. I would like to change "Contemporary Issues" to "Contemp Issues" and "Administration" to "Admin".

Where do I make the change and what effects will it have? For example, will all the posts in that were posted in Contemporary Issues still appear with the name change?