Yes you may edit an item after uploading it to your user store in order to make changes to the image, and also to change the prices of your items.

To do this just go to your own user store and you will see the edit option listed under each item in your store. After uploading and upon the change being approved you may refresh your browser to see the new image by hitting control and F5 keys at the same time.

Please keep in mind though like item uploads, editting prices also have to be approved by an items editor, so please limit your changes to 10 items or less at a time untill those items have been approved before making more changes.

When you see that those items have cleared, then you may continue to make price or other changes.