How was king ducan killed?

King Duncan was killed by Macbeth in the latter's castle at Inverness.

The king was asleep in his chamber which had two guards outside whom Lady Macbeth had given intoxicated drinks.

Note : Due to Macbeth's prior decision of not killing Duncan, Lady Macbeth had decided to take up the 'business' . However, when she saw her father's face in Duncan's, she decided against killing the king herself.