To edit a product is easy. Simply go to your Products page and click on the title of the product you want to edit.
You can also select the "Edit" option under the Actions dropdown.
You'll then be taken to the same workflow as when you created your product in the first place. The only difference is everything is filled out now.
Simply edit the attributes you want to, and then don't forget to click the "Save changes" button at the bottom of the page once you're done.