I would recommend the WordPress SEO Plugin by Yoast: http://yoast.com/wordpress/seo/
I believe there is also a video tutorial website for the plugin.
You may need to hire an SEO consultant or online marketing firm to take the website to the next level though. I noticed that the pages load kind of slow and the titles and content aren't yet optimized for the search engines. You could use this list as a guide to online marketing services: http://online-marketing-services-review.toptenreviews.com/
Or you could also search for local companies to work with you in person. I know that there are a lot of SEO companies in India and Asia.
To do the SEO work yourself you can gain more knowledge of SEO from a video tutorial website like Lynda.com and then try reading 'The Art of SEO'. You use the SEO techniques in conjunction with the WordPress SEO Plugin by Yoast.
Good luck with your online business!