problem with articles letter text

Hi!
When i created an article on blog and i want to chance the letter text, I can choose between, paragraph, title 1, title 2 ecc.

When I wrote (with admin)and chance the text, for exemple, from “paragraph” to “title one” the text has changed, but when I saw the preview or the saved page on website, the letter text is always “paragraph”.

how I can solve this problem?

Thanks