Thank you for your reply.
1. It only shows true to size when you open the website on bigger screen.
On my standard full HD 13 inch laptop, the logo looks low-res.
2. I have changed the setting to full-width, the problem is still there.
3. Another problem is sometimes the header breaks in half as in the attachment.
Could not install the plugin with the way you told me. I went to File Manager from Cpanel, deleted the old files in revslider folder and upload new plugin zip file. It works then.
Thank you by the way.
I found out the problem caused by plugins. I have deactivated a few plugins and that solved the issue. Thank you.
