Hey Hasan,
Sorry for the delay.
John here stepping in for Muhammad. I had a look into your site and it appears that you are using a static block for your footer. To alter the logo, you will hence need to edit that static block and specify your preferred logo. Here is a screencast on this: https://recordit.co/AjB4i74wju.
Let me know if you have any questions.
Best Regards,
John