Hi ravsumeet
To change the width of the search bar Try adding the following CSS to your Quick CSS (located under the Styling Tab in the theme options) or the custom.css file in the css folder of your theme files:
.search_site #searchform #s {
width: 70%;
}
Next you need to open js>avia.js in your theme files and search for:
jQuery(".main_menu .search_site").avia_expand_element({expandToWidth:300, speed:800});
Replace it with
jQuery(".main_menu .search_site").avia_expand_element({expandToWidth:367, speed:800});
You can edit the mega menu in Appearance>Menus in the wordpress admin. To add images, you'll set up the basic mega menu like in this video:
http://www.kriesi.at/themes/abundance/templates/video-tutorials/#menu then you can make a new menu item with the URL set to # and in the Description field of that item you'll put in the html for an image and a link:
<a href="http://www.yoursite.com" ><img src="http://www.yoursite.com/yourimage.jpg"></a>
I think the first widget in your sidebar is causing the rest of your widgets to be incorrectly scaled. If you can put in the QR code image without using an iframe it should fix the issue. Making the sidebar wider would cause the entire site layout to need to be redone.
Regards,
Devin