Google found me this list of athletes with medals both winter and summer:
* Eddie Eagan, USA (2/0/0)
SUMMER: Light Heavyweight Boxing gold (1920)
WINTER: Four-man Bobsled gold (1932)
Eddie Eagan became the first person to win a medal in the Winter Olympics and in the Summer Olympics in different events. He is the only Summer and Winter medalist to win Gold medals in different events.
* Jacob Tullin Thams, NOR (1/1/0)
WINTER: Ski Jumping gold (1924)
SUMMER: 8-meter Yachting silver (1936)
* Christa Luding-Rothenburger, GDR (2/2/1)
WINTER: Speed Skating gold at 500 meters (1984) and gold 1000 m (1988), silver at 500 m (1988) and bronze at 500 m (1992)
SUMMER: Match Sprint Cycling silver (1988)
She is the only athlete to ever win medals in both Winter and Summer Games in the same year.
* Clara Hughes, CAN (1/1/4)
SUMMER: Individual Road Race Cycling bronze (1996), and Individual Time Trial Cycling bronze (1996)
WINTER: Speed Skating gold at 5000 meters (2006), silver at Team Event (2006), bronze at 5000 m (2002) and bronze at 5000 m (2010)
Clara Hughes is the first person to win multiple medals in both Summer and Winter Games and holds the highest number of medals of any olympian to win medals in both the Summer and Winter Games.
* Lauryn Williams, USA (1/2/0)
SUMMER: Athletics 4x100 m Relay gold (2012), and 100 m silver (2004)
WINTER: Two-woman Bobsleigh silver (2014)