All existing blog post information will be replaced with the new data. To avoid deleting all existing data, retrieve any data you want to retain first, and send it back with this request. For example, if you want to add a new tag to a blog post, retrieve the existing tags, and send them all back with the new tag in the update request.
To update a blog post, complete the following steps:
1. Retrieve the Blogs service document. See Retrieving the Blogs service document.
2. In the service document, find the workspace for the blog from which you want to retrieve the post, and then retrieve the web address of the "weblog Entries" collection in that workspace.
3. Send a GET request to the weblog Entries collection.
4. In the returned feed, find the entry and note down the value of the href attribute of its <link rel="edit" type="application/atom+xml" ... >
5. Send a PUT request to the web address defined in the href attribute and pass in a new blog post entry document that includes your changes.