How to Set default shipping option with script

Click on Design > Themes. Click on the active theme you are using.
Click edit header
Click source in the rich text editor box. Paste the script previously copied to the bottom.
Go to whe
From the scripts folder copy the script for the default shipping options Script Library.
re it says var value = '4292634'; // ID of the shipping option and change the 4292634 to the shipping code relating to the option you want to be default, see below:

To find the shipping code download firebug for firefox
go to your storefront and place a test order with firebug enabled.
At the shipping options checkout page look in firebug and at the very top left side there is a rectangle box with an arrow right to the left of the firebug.
Click on it, then click on the shipping option you want to be the default choice. It will light up in the firebug box and you'll see a code similar to the 4292634
Replace that in your code and apply and save theme settings
Refresh the shipping options page to see your new default shipping option chosen.