Click on your Profile Icon on the top-right hand site, then click on MY WORKS on the dropdown. You will be redirected to MY PUBLICATIONS page
Hover your mouse on PUBLISH. Then click on MY PUBLICATIONS
You will see all your published books
Locate the book you'd like to edit or update it's cover. Click on the PENCIL icon in front of the book
The book edit page will open up.
Scroll down PRICE to change it. If you would like to price your book for N400, just enter 400
Once changed, click on Republish to republish it