For instance, you have a product SKU 10001 ("Planet Express Babydoll") for which you need to reduce the price from $19.99 to $9.99, and a product SKU 10007 ("Electronic Drum Kit Shirt") for which you need to increase the stock level from 5 to 15 units. Let us first consider the most uncomplicated case when these products don't have options or variants.
The process is pretty straightforward:
Use the CSV Export page of your store's Admin area (Catalog > Import & Export > CSV Export) to export your existing products. Also, see the general export guides here.
Download the resulting export file and open it in any spreadsheet editor to view the file contents separated into columns.
NOTE: For the sake of example, we'll do it with Google Sheets on Google Docs.
The file you get has many columns, so removing the columns you don't need to update makes the file more manageable. However, please be careful not to remove the columns that are required.
To find the required columns for your file, check the CSV Import: Products guide. The table describing the data format for importing products shows only two required fields (marked with asterisks): sku and name. So you will need to keep these two columns. In addition, you can find the price that needs updates in the column price and the product quantity - in the column stockLevel. So, you will have to keep these columns as well. You can safely remove all columns except sku, name, price, and stockLevel.
NOTE: If you need to update other price values, use the following columns:
costPrice - the products cost price;
marketPrice - the product market price;
wholesalePrices - the wholesale product prices;
sale - a product discount set either in an absolute value or in a percent;
saleDiscounts - the global product discount.
After you do so, your spreadsheet should look something like the following:
NOTE: On the screenshot above, the column name has the name name_en because it contains values for the English language; the column name will have a different language code appended for other languages.
On the SKUs' lines for which you need to update the price and the stock quantity, edit the contents of the price and stockLevel fields as you require.
Save the file and re-import it into your store via the CSV Import page in your store's Admin area (Catalog > Import & Export > CSV Import).
After completing the import process, you should see the updated product information in the respective products' details.