How do I use CSV Import to update prices?

The best way to update your prices would be to first use the CSV Export feature and export a few fields.  I suggest Product Title, Product description & Product Handle & Price.

Open this CSV file in a spreadsheet application and edit your prices. Save your file.  

Use the CSV Import feature and upload this updated file.  Use column 1 as Product ID to search.  Use the column # associated with your Price column to update Price.