All you need to do is go to Seller Admin > View/Edit/Delete Products, select that product and press Edit. On that first page you can simply change the price that is listed there.
While you have the option to upload a new file or change other settings that is not required. Just be sure that you proceed through all of the Next buttons until you can Submit your changes, or the price will not stick.
There's nothing else you need to update. We tell PayPal what the price for any given item or order is when we send the order to checkout, so you never need to enter prices at PayPal directly.