Are you talking about shedding skin or shedding shell?
A certain amount of both is normal. Too much shedding of skin is often caused by water temperatures too high. For an adult RES, the temp should be at around 75 degrees.
http://www.redearslider.com/water_temperature.html
It would be very helpful to post a picture. Usually, shedding skin is best seen while the turtle is underwater.
For shell problems, the best way to show is with a photo of the dry shell.