Can I change a post's URL?

Yes. The part of the address after your blog's domain is the post's slug.

1. Open the post, and in its settings click Slug.
2. Enter the new slug, for example guides/getting-started. It can contain lowercase letters, numbers, dashes and slashes. Keep it under 60 characters.
3. Click Save slug, and deploy.

Superblog does not redirect the old address for you. If the post was already published, add a redirect from the old slug, so existing links and search rankings carry over.