It depends on what you changed. Sometimes it is a cache issue (i.e. it just takes time) and other times there are other thing you need to change as well. If you could provide more details about what specifically hasn't changed that you expected to, we would be able to give you a more specific answer. In the mean time, I will provide a generic answer that covers most cases I have seen.
There are typically 3 places users mean when they refer to the "wiki's name".
- The domain in the URL. For example, "community" in "community.fandom.com".
- The system message typically accessed using "{{SITENAME}}". For example, Community Central.
- The name that appears in the local navigation bar above all the menus and to the right of the wordmark. By default, the same as #2.
In order to change #1 and #2, you have to send a request to Wikia staff. This can be done using this form. For #3, admins can use Help:ThemeDesigner.