If it's a plain background, use the magic wand to select the area you want to remove. It will pick up a colour range determined by the sensitivy slider. Hold the shift key and click another part of the background to add to the selection. A low sensitivty will only select the colour you click on, and a higher setting will widen the range of shades. The only problem with this method is if the subject is the same colour as the background it will also be selected.
Another magic wand method is to use it to select the subject , then invert the selection and delete, leaving a plain white background. If you find the magic wand tool is too fiddly, go to Select > Color Range, click on the subject and use the slider.
Or you could use the eraser tool to maually remove most of the background, then zoom in to the outline of the subject, use a smaller eraser and carefully go around it removing the remaining background areas.