I�??ve been asked by a colleague to increase the size of a text field in a GeoDatabase. I cannot see a way of doing this without creating a new field which means the field order will be messed up and I will have to chose a different field name too!
That's the only way you'll be able to do it as far as I know.
Since the order of your attributes is important, I suggest creating an empty feature class of the same type, and create the attribute table just like the one you have, but when you get to that particular attribute, make it the length you need. Then you can use the simple data loader to load all your existing features into the new feature class.
If you are working in a versioned sde environment this approach is going to s**k. If it's a file geodatabase or a personal geodatabase it's not to painful.
Acutally, if it's a personal geodatabase, you can open the attributes table in access and change the field length there. Nobody likes to admit you can do that, but you can; just back up your data first....