Carrie Underwood returns to American Idol on Tuesday (May 19) to perform this year's Idol farewell song, "Home Sweet Home." The two-part season finale takes place Tuesday and Wednesday (May 20) as the winner is determined between finalists Adam Lambert, 27, of San Diego, Calif., and Kris Allen, 23, of Conway, Ark. Underwood won the competition during its fourth season. Her version of the MÃ¶tley CrÃ¼e song, "Home Sweet Home," has aired on American Idol this season as the goodbye theme for contestants leaving the show. Underwood, her record company and iTunes are donating a portion of the sales proceeds of the "Home Sweet Home" digital single to the Humane Society of the United States. The donations will be used directly for programs that help companion animals, including spaying and neutering services and the rescue and shelter of animal victims of puppy mills and disasters.