[SM-A510F] Flashed with stock firmware, don't have internal storage space

So i flashed my SM-A510F with stock firmware, cause i got the ''custom binary blocked by FRP lock'' error, had about 2,5 GB free. After I unbricked my phone, I only had 600 MB. Mb it's just the old firmware didnt get deleted? I had Android Lollipop, and when i unbricked my device it updgraded to Marshmallow. I'm new to this stuff, so plz help meh :D

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