이름이 뭐에요? ii-r-mi mwo-e-yo?
(most common polite expression, you can use this for everyone but usually for same aged or older person, stranger.)

이름이 뭐야? ii-r-mi mwo-ya?
(friendly expression. use to younger person, friend who allows you to use plain terms)

성함이 어떻게 되세요? seong-ha-mii eo-ddeo-ke doe-se-yo?
(really really polite expression, you can use to stranger, senior citizen, your boss and anybody you want to express your reverence to)