How to add a logo to Ally?

You can upload a Logo through the Customizer. Go to Customize > Header Image and you can upload your logo from there.

The default size is 360 x 164, so if your logo exceeds that width/height, then WordPress will make you crop your image. If you want to use a different size, then you can change the size in your functions file. Should look like this –

// Add support for custom header
add_theme_support( 'genesis-custom-header', array(
	'width' => 360,
	'height' => 164
) );

Let me know if that helps, or if you need any assistance uploading it.