Answers

Nov 23, 2015 - 09:26 AM
Yes you can use the batch update fields to update your existing data. it is always recommended that you export your data out so you can get the product ID so you can easily prepare your update sheet with the changes and upload the data.
you can review the fields information here for batch update.

Nov 23, 2015 - 09:26 AM
For more detailed information about Batch Update please review Tutorial No. 1.26 Demo of Using Batch Update, and Tutorials No 1.25 Add/Modify/Delete Products with Batch Update