first of all, let me recommend to update your Embedded Wizard Studio / Build Envrionment for the STM32F746 to the latest version. There are so many changes between version 8.10 and 9.00.
In order to change the display, let me refer to the article 'Bring-up on customer specific hardware' - which explains all the necessary steps when porting a provided Build Envrionment to a similar hardware.
Concerning your questions:
1.) From Embedded Wizard Studio point of view, it is necessary to change the attribute ScreenSize of the profile and to adapt your screen design in order to use the new space :-)
2.) Yes you can do that with the Free Evaluation Edition.
3.) Changing the display size makes only sense if you are using the new space. I think you will modify/redesign your sceens - the entire control logic will not change.