How to modify the face (e.g increase eyes or lips)?

You can modify the face with morphing, i.e. changing the base model of the face. Please, mind keeping the UV coordinates unchanged.

Put the FBX file with the changed geometry in the SRC folder. Go to the Filter Editor, point to the file warp_mesh and turn off the display of the corresponding material. It's better to morph a face gradually checking the results of your work in the editor's viewport.