You can change the blog post title and/or description in its general settings.

NOTE: Blog post title and description are automatically used as meta title and description

Within the editor, open the blog management panel on the left and find a post that you want to edit. Click on the ellipsis button ⋮ near the blog post title:

Click Settings:

Change the title and/or description in the general settings tab:

Save the changes and update your website for the changes to reflect online.

NOTE: Learn more about managing blog settings