You should upload a PNG file which has transparent background. If you are going to use Adobe Photoshop, pls check the transparency option while exporting the image as PNG. Let me know if you still have trouble. Thanks
Can you either post the URL here or email me through my themeforest profile page the URL for the page? I checked locally here and there is nothing in the code which is hampering the transparency. In fact, the theme logo you see in the demo site itself is transparent and when you change the color of the background, things look normal. Thanks
I checked the logo in Photoshop. It is not transparent. It has white background and hence you are seeing it in the header. You need to ask the company that gave you the logo to provide a transparent one. Or you need to make your header background white.
I have taken your logo and made it transparent just as an example.
You can see the difference by using the transparent logo in your header.