Hey Joanna,
Thank you for reaching out to us!
If you simply change the title of an existing post, page or event in WordPress, it won’t automatically update the permalink. I know there are plugins that can make this change for you, but it’s not an out-of-the-box feature in The Events Calendar.
If you duplicate an event and change it’s title, you’ll have to update the permalink for that specific event as well.
If you have any other questions at all please feel free to let me know and I’d be happy to help as best I can!
Cheers,
Patricia