You can quick edit product Quantity and Prices as follows
To view your products simply go to the products list view page by clicking on Products in the menu on left of your User Interface.
If you're already logged in, you can simply click HERE
Now you'll see a list of your products.
You can simply change the values in the QTY and Price columns.
Once you've made the changes you can click on the Save All Changes button at the top right of your screen