How do I change post formats?

Hi,

I would like to change my posts from “the whole thing” to just the title, the first paragraph with a picture. When the reader clicks the image or the title, they go to the full text. I have tried changing the format in the Edit Post pane, and the option that says: “For each article in a feed, show” to “Summary”, but neither seems to have worked. Is this a premium feature?

Thanks in advance

Elise