How Do I Change My Product URLs
You can create "cleaner" URLs for your products by using the Rewrite Url To feature.
In the Admin
This input rewrites the URL for the product to the specified text. For example: A standard URL for this page may look like "http://www.mystore.com/teeshirt001_black.aspx". A store admin could rewrite this URL to "http://www.mystore.com/shirt.aspx" by entering "shirt.aspx" in the Rewrite URL field.
The first thing you will want to do is perform a product export using only (sku & Product URL)
Next, you will change the producturl column header on your spreadsheet to rewriteurl and change the URLs to whatever you want them to be.
Finally, you will import your spreadsheet using the product importer.