How can I edit an already submitted DS-160 application? I have already paid for the visa fees and the portal has changed

How can I edit an already submitted DS-160 application? I have already paid for the visa appointment and scheduled a date and now the portal has changed. I cant seem to find the update information section. Will i have to make the payment again and book appointment again? Also, i have added intended length of stay as 2 years but my course duration is 16 months. will that be an issue