1. Obtain your data by performing an export of the objects you wishto update, or by running a report. Make sure your report includesthe record ID.
2. As a backup measure, save an extra copy of the generated CSV file.
3. Open your working file in a CSV editor such as Excel, and updateyour data.
4. Launch Data Loader and follow the update wizard. Note that matchingis done according to record ID. See Insert, Update, or Delete Data Using Data Loader.
5. After the operation, review your success and error log files.See Review Data Loader Output Files.
6. If you made a mistake, use the backup file to update the recordsto their previous values.