How to reduce first byte time

[ramji.guru99]

Hi all,
I have developed a joomla 3.2 site. I have tested it with webpagetest.org and i got following results
First Byte Time-F
Keep-alive Enabled-A
Compress Transfer-A
Compress Images-A
Progressive JPEGs-F
Cache static content-A
Effective use of CDN-yes

link for the result-http://www.webpagetest.org/result/140205_RX_DE5/1/details/
http://www.webpagetest.org/result/140205_RX_DE5/

I have enabled cdn on my site.Now, I want to reduce my site's first byte time as i'm getting F in First byte time. how can i improve my site's performance??
And, how can i convert images to progressive images as i got F in progressive JPEGs??
Here's link to my site-http://www.guru99.com
Please help me to improve site performance.

Regards