To change the price on any of your products you must change the price in your "Add to Cart" buttons. This will need to be done in the HTML code on your web pages.

Find the price of the product in your "Add to Cart" code and change it to the new price. The price is saved in Field 3: itemcost (required).

Go to this setup help page:
Add to Cart Codes Explanation

Alternatively, you can use the Button Builder to build a new button for the product with the new price, and replace the old button entirely.

Note: If you have Secure Product Information Using Inventory Control enabled then you will need to edit your prices using the Inventory Control tool in the shopping cart administration.