I have the succulents theme. I have installed my logos in the select options> logos section of the WP Admin pages. There were no demo logos in there and now mine are all uploaded and visible .png files, but they will not show on the preview or actual site and the demo logos are still there.
Please check the Item documentation hopefully you will get necessary support. Otherwise the best way to get the support is Contact your purchased Item Author. How to Contact Author and let them know because Item Author are best expert about their Item functionality. Don’t worry just contact Author. Author will be very happy to assist you.
Also you can check your theme Options if you find anything related to the issue.