While both past and perfect are possible, it is natural to use perfect (has released). The release of the ep is a past event with consequences in the present (you knowing about it) You are talking of the present state of the ep, rather than about a past action. We don't care about exactly when it was released. Present perfect is the tense used in this situation.
I've just heard that he has released ep "bla bla bla"
If you changed to talk about a past time the use the past tense
I've just heard that he released ep "bla bla bla" yesterday