When you first upgrade to Ripl Pro, you'll be asked if you want to upload a custom logo. If you choose not to upload at that time, you can update your logo anytime in your "Business Profile Settings" in the Ripl menu. You can also update your logo on a post-by-post basis by tapping the logo on the "Customize" screen.
In your Business Profile Settings, there is also a toggle switch to display or hide your logo in your posts. If you opt to include your custom logo, you can still hide it on an individual post by clicking your logo in that post and following the prompts to hide your logo for that post.