This is what your Twitter profile page currently looks like. This guide shows you how to update your profile page to the new twitter profile layout via the web.
The new twitter profile page is actually live, but to activate it you need to upload a header image to your profile. First click on settings.
On the settings page select the design tab.
Scroll down the page and find the change header button. You will notice the recommended dimensions of 1200X600. The reason this is so large is to accommodate retina displays on the iPad.
You can select any large image you wish but I made an image ahead of time at the exact dimensions listed on the previous page. Browse on your computer and find the image that you wish to use.
After you have selected your image, Twitter will give you the option to scale and position your header image.
You will now see that your image has been uploaded and a thumbnail preview is in the header upload area.
Lastly click the me tab at the top of the website to preview your handiwork. Congratulations, you are now Twitter famous.