Hi there. To the people who you would like to show a certain level of respect, you would say: 안녕 하십시요!(an-nyeong-ha-sip-si-yo) or 안녕 하십니까?(an-nyeong-ha-sim-ni-gga) For general people or strangers, we usually use: 안녕 하세요!(an-nyeong-ha-se-yo) In a bit informal situation, we may sometimes say: 안녕 해요!(an-nyeong-hae-yo) or 안녕 합니까?(an-nyeong-ham-ni-gga) [Native speakers, please rectify it should this presumption be wrong.] For people who well know each other, we simply use: 안녕!(an-nyeong)