Why we can't convert Master detail Relationship field to Lookup Relationship Field having Roleup Summary Field?

Hi Suraj,

if A is master of B then if you need to change this master detail relationship to lookup then you only need to click on setup -> objects > master detail field > Edit > now you will not be able to see button "change field type" if there is Roll up summary field on Master object so delete it first and also remove it from "deleted fied" trash box then you will be able to see"change field type" button.Once you remove it from trash box change field type will be available to you.Just click on it and change it to LookUp Relationship.

Thanks.