How did Macbeth kill king Duncan?

when Macbeth and banquo were returning from the battlefield, they met the weird sisters who prophesied that Macbeth will be the thane of glamis, thane of cawdor as well as the future king of Scotland. since after returning from back Macbeth was proclaimed thane of cawdor, he became ambitious and wanted to be the future king of Scotland. therefore when duncan came to visit Macbeth to honour him for his outstanding bravery, he instigated by lady Macbeth murdered duncan