The phrase "to refine the design" means to improve or make changes to the original plan or layout in order to make it better or more efficient. Full definition
On the needs improvement side of things, the firm should consider a little more refined design of the app's pages, particular the main «home» page. (lawfirmmobile.com)
Changes also carry on inside with a more refined design of the dashboard, though much of the theme remains the same. (autonationdrive.com)
He invited the industry to work with his government to «further refine the design principles of such a scheme». (smh.com.au)