Let's get started on how to update your price in KDP (Kindle Direct Publishing)!
Visit Your KDP Bookshelf (https://kdp.amazon.com/bookshelf)
Locate the book you want to update
Click the ellipsis button ("...")
Choose Edit eBook Pricing
Make adjustments in the Royalty and Pricing section
When ready, click Publish Your Kindle eBook at bottom of screen
Update times may vary. For ebooks, it may take up to 24 hours. For paperbacks and hardbacks, 3 to 5 days.