Best way to do it is through EXTRACT.
Depending on your version of Photoshop, It should either be in the Filters menu or the Layers menu as "Extract".
You then have 4 tools to use to your advantage.
The first one is your highlighter tool. you will use this to highlight the edges of the part of the image you want to cut out. Once you have created a complete circle with no holes, you will want to select the bucket tool and click anywhere inside the image you want to keep. It should fill u[p everything you went around.
You can then go on to hit preview to start the extraction process. Once you have the image with the background out, you can then use the next 2 tools. The Edge TouchUp and Clean Up tool to smoothen and erase parts of the background that was still left. This is by far the most acurate way to extract a background. It's fast and it can really make a differnce when you got a deadline.
Or you can use Cut Out. It's a PhotoShop plugin you can find anywhere on the net.
Holler.