Requirements:-

• Mozilla Firox
• Live HTTP Headers Add On for Firefox
• A shell

So now lets begin,

• Login to that site as a admin, then find a place to upload a file in that particular site.
• Then rename your shell name to shell.php.jpg (or what ever that site supports. In my case, site supports only jpg file. Thats why i renamed it to shell.php.jpg.)
• Then start your Live HTTP Headers addon, after that upload your shell.
• Then your Live HTTP Headers will look something similar to this
  
  
• Then click on the shell.php.jpg, after click on Reply button.
• Then again a new window will open, in that window there will be two boxes, but we have to work on second box.
• In the second box, rename your shell.php.jpg to shell.php, then again click on Reply button.
  
  

Now you have successfully done, only thing you have to do is to find the shell path.