Improving PHP/ MYSQL Admin Database to run Mobile Phone Shop

I have a PHP/MySQL script to Add, process and search Customer info for a mobile shop business. It has some problems which i need to be corrected. I want to make it configurable and make a good design. The pages in script are Add Customer Update Customer Delete Customer Add Cash Back In Progress Search Change Password The Html flow will be provided, and the script which has been done already will be given too, to start work.