Thank you maxter.
Your reply to my query is near to resolve the issue, but I think it needs further tuning. Because, just moving the section alone in tpl file may not serve the purpose, as the radio button which not clicked will auto populate the guest details in the shipping field. In the invoice page also the details entered by the user has to be reversed. But if we move the the section alone to top it may not work as we needed. Kindly guide me exactly how to achieve it.
Update: I tried moving the shipping section in tpl file to the top as you said. But still the checkout page shows billing address field in the top, despite clearing cache in admin panel and browser. I request all to help me regarding this.
Thanks
AVS