Hi mikiyas yosef,
The video posted by @timtomissus is for the Galaxy Core Prime rather than the Core Prime Duo, but the procedure is the same.
The rear cover simply snaps off; there's no glue or screws holding it on. Put your thumbnail in the little slot on the bottom of the battery and lift up. Here's another guide with step by step instructions.
[link|https://www.nadiemellamagallina.com/en/manuales/smartphones-1/samsung-4/samsung-galaxy-core-duos-100/bateria-538|Manuales / Samsung Galaxy Core DUOS / Battery|new_window=true]