How can I remove the JotForm branding from the thank you page?

Also how can I not have a thank you pop up or just say Thank you?

I am not sure if I understand your question correctly. If you are looking for redirection user to a different page than thankyou page, then please follow the instructions provided at https://www.jotform.com/help/38-Redirecting-Users-to-a-Different-Page

Hope this helps.