Please turn on the dev mode then reload.
Then give us the screenshot of the error that is shown.
To enable the dev mode to go to your QloApps folder --- > config --> open define.inc.php file.
Then on line 29 change define('PS_MODE_DEV', false);
to define('PS_MODE_DEV', true);
Please increase the value of memory_limit to 500 once on your server and try to upload the images again.
If the issue persists the please create a ticket at https://webkul.uvdesk.com with your Admin login details and FTP credentials.