Should have made myself clearer. I have tried to upload a photo but the dimensions are all wrong and the picture then looks nothing like it should i.e. distorted. Are there set dimensions a photo should be to make it compatible to go in a slider.
For width: it depends on what size layout you have chosen in theme options.
For height: You can also set the featured slider height within Canvas. If you go to Canvas / theme options / business template / Featured slider. At the bottom you will see the option to put in a custom height for your slider.