It's very easy to connect your form to a thank you page or up-sell page.
Step 1
Click on the button of the form
Step 2
Click on the chain icon
Step 3
You have the option between URL and Message. Choose URL.
Step 4
Here you can enter the succes link and failure message. A failure message is probably not needed. This is only necessary if there are some problems from the user's browser side.