http://www.sammobile.com/firmwares/database/SM-G3815
Aqui te descargas la rom si eres de españa descarga la española libre que seria esta:
http://www.sammobile.com/firmwares/d...15OXXCNL2_PHE
abajo de la pagina te pone las intrucciones
Extract (unzip) the firmware file
Download Odin v3.10.6
https://mega.co.nz/#!epshkJAa!y7pFS5...B_9mDZWfXkLqko
Extract Odin ZIP file
Open Odin v.3.10.6
Reboot Phone in Download Mode (press and hold Home + Power + Volume Down buttons)
Connect phone and wait until you get a blue sign in Odin
Add the firmware file to AP / PDA
Make sure re-partition is NOT ticked
Click the start button, sit back and wait few minutes
Pierdes todo asi que pasate las cosas personales primero al pc