look like worked with you to fix this issue.
the update will not run the install process again., you will only need to upload the updated files to the server.
I believe the issue with the redirect would have been fixed in the webassist/shopping_cart/checkout_form.php file, it is likely that updating will overwrite the change that was made.
before updating it is always a good idea to make a back up so that if anything goes wrong, you can revert to a working point.