Just to the left of the web address is an icon, called a favicon. Sometimes the favicon is just a blue orb and sometimes it is an icon that represents the site. (ie, on Apple.com, the favicon is the Apple logo.) Click once on the favicon and the entire address will become selected (turn light blue). You can just start typing your new address. The first key you kit will clear out the old address so you can enter the new one.
If you prefer keyboard shortcuts, doing a Command-L does the same thing as clicking the favicon.
As a reminder, it is not necessary to enter the "http://www." part of a web address. Just type in the main part of the address, ie "apple.com" and you will be taken directly there, Related Items: Safari