изменять -- imperfective aspect изменить -- perfective aspect

"Изменять" is repeating action of changing. To change smth or smbd for a long period of time. "Изменить" is only one action instead of many as in "Изменять". "Изменять" is like the Infinitive "to change".

There is no any difference absolutely.

Фарид, consider this family of words: менять - imperfective. Means менять-1) + accusative - 'to change [something]', i.e. to make something different. менять-2) + acc. [+ на + acc.] 'to exchange, to barter, to swap [something for something'. ИзменИть - perfective изменить-1.) + accusative. - most common perfective counterpart for менять-1. изменить-2.) + dative or without a noun object. - to became unfaithful, to commit adultery, to break an oath etc. Usually is used in the sense of adultery. изменить жене/мужу. Изменить слову (break a promise) ***There're ohter ways to form perfective from менять: поменЯть - 1. perf. from менять-1 with slightly different shades and for slightly different contexts that изменить. 2. perfective from менять-2. переменИть - rarely used perf. for менять-1*** ИзменЯть - impervective again! изменять-1 + acc. - (rare) = менять-1. It's used rarely in this meaning because we have "менять" which means the same. If one choses this form, (s)he may point on 'getting the result of changes' as opposed to being focused on the process of changing. изменять-2 [+ dat] - imperfective from изменить-2. So, answering your question as you've stated it: In most cases when you hear 'изменять' it's изменять-2. An adultery etc. While изменить may be изменить-1 as well as изменить-2. изменя/ить-2 is used with dative or without a dependent noun. изменя/ить-1 - always comes with accusative.

"Изменять" also "betrayal" Муж изменяет жене.