They have some overlap in meaning but not that much. 인격(人格): the whole character and moral make-up of a person; integrity 성격(性格): characteristic traits of a person's personality; character; disposition So 인격 is what makes a person a respectable human being, the (intangible) make-up of a person. It is only talked about in certain contexts like 인격의 문제, 인격을 침해하다/모독하다/존중하다, etc. You almost never say 인격이 나쁘다/좋다, etc. 성격 is just a trait of personality, much as a hair color is. It varies widely, so people might have 좋은 성격, 나쁜 성격, and 이상한 셩격. You may say 쟤는 성격이 나빠, 너는 성격을 고쳐야 돼, or even 성격 좀 바꿔라.

인격은 사람의 가치를 말합니다. "인격" means the value of human. So we can distinguish the good person and bad person. 예를 들어, (for example) 그녀는 훌륭한 사람이다. - She is a wonderful person. 그녀는 좋은 인격을 지녔다. - She has a great personality. These are the same means. 그러나 성격은 개인의 특징을 뜻합니다. But "성격" means an individual's characteristic. 예를 들면, (for example) 그는 잘 웃는다, - He laughs well. 그녀는 항상 빠르게 말한다. - She says always fast. 나와 그녀는 성격이 너무 달라. - She and I have a character so different. In "성격(character)" exist the only distinction, there is no good and bad. But some people says "너 참 성격이 좋다!(Your character is good! or You have a good character!)". But it is not a good expression. They have to say "너의 성격이 참 마음에 든다!(I like your character!). I'm so sorry, my english is very poor. I hope that you will understand very well.