How Did Lord Ganpati Get Elephant Head?

Parvati, the wife of Lord Shiva was alone at home and wanted to have a bath. To guard the entrance Parvati created a human child - Ganesha - out of the earth and asked to guard the entrance while she took a bath. While Parvati was bathing, Lord Shiva came and wanted to enter the house. However, Ganesha blocked him from entering saying that it was his mother's order not to allow anyone inside the house. Then, Lord Shiva became angry and cut off his head and entered the house. When Parvati saw that Lord Shiva cut off his head and then Parvati told what had happened and then even Lord Shiva felt sad. Then Parvati told Lord Shiva to go to the Himalayas and cut the head when he sees the first animal and then to splice it onto the headless body of Ganesha. The first animal that Lord Shiva found was an elephant, that is how Lord Ganesha's came to have an elephant's head.

This is another story of Ganesha:

When Ganesha was born, his mother, Parvati show off her new baby to the other gods. Unfortunately, the God Shani (Saturn) who is said to have an evil eye, causing the baby's head to be burned to ashes. The Lord Vishnu came to the rescue and misplaced the missing head with that of an elephant.