I think your question addresses two different aspects:
1.) Porting a GUI designed for screen size of 240x320 to a screen size of 480x272
2.) Porting a software project based on CubeF4 firmware with an initialization for STM32F429 and the different hardware components on the STM32F429 discovery board to an STM32F746 and the different hardware components on the STM32F746 discovery boards.
In case of 1.) you can change the ScreenSize of your project and rework your project so that the GUI application will use the additional space. But this is more a question of GUI design.
In case of 2.) it will be the best to start with a new project based on the Build Enviornment for STM32F746 Discovery.