This tutorial shows how to remove quantity box on the product details page in Magento.
Open /app/design/frontend/tm_themes/themeXXX/template/catalog/product/view/addtocart.phtml file in your editor. Alternative path to file is the following (it depends on the template): /app/design/frontend/default/themeXXX/template/catalog/product/view/addtocart.phtml (themeXXX is actual theme name).
Look for code that looks like on the screenshot below (div may have another class in your template). Remove the code:
The modified file looks like on the screenshot below:
Save changes and upload the modified file to your hosting. Refresh the page. Quantity box was removed:
Feel free to check the detailed video tutorial below: