If you built your Wix website a while ago, you may have the old Wix Blog format and so you will need to switch to the new Wix Blog with a whole host of new features and designs to make your blog look better than ever.
Steps to start the transfer process: (see https://support.wix.com/en/article/information-on-switching-from-the-previous-wix-blog-to-the-new-wix-blog for full details)
1. Copy your old blog posts
2. Update the URLs of your blog posts
3. Delete your old blog and publish the updates (see https://support.wix.com/en/article/deleting-the-old-wix-blog for instructions on how to delete the old blog).