Original: The second stage will be either a Briz-KM (Angara 1.1) or Block I (also called URM-2), which is powered by the RD-0124A engine developed by the KB Khimavtomatika. Angara 5 will use either the Briz-M upper stage (currently used for the Proton-M rocket), or KVRB.
Simplified: The second part (called the second stage) of Angara 1.1 is called Briz-KM and the second stage of Angara 5 is called Block I.