From the main menu strip at the top, go to Setup > Items.
Click the Options button located at the top right.
Click Import Items CSV from the Options button dropdown menu.
Step 1 - Click the Browse for Items CSV file to locate the csv file on your local hard drive.
Step 2 - Click the Preview Data button to upload the file and preview the data.
Step 3 - Set the Import Mode toggle to the Update option.
Note that to avoid any accidental updating of existing field data, any of the columns that may have been auto-matched based on the column name will now be unmatched, except for the Code column (which is a required match for updating items). Step 4 - Now you can manually choose any other columns that you wish to update in the Belongs to... section. Your item data will only update if you have matched the column and there is a value present to import, otherwise your existing data will remain untouched.
Step 5 - Click the Import Data button to complete the process and update your item data.