Replacing/changing video background
That's a tricky one since the background color is the same as the shirt shes wearing. This can be achieved Manually by masking your subject frame by frame, if there is no much movement and duration is little then this shouldn't be a problem, although you might have some difficulty with the hair.
Note: masking should not be very accurate in this case, make a fast one then feather it and increase the brightness of the layer behind "background" until it becomes bright white and see if you like the result.