How to flash stock ROM on Galaxy Young So I had a perfectly rooted Galaxy Y w/ Android 2.3.6, but then I can't remember why, but I changed in some system files and my device is no longer rooted. I've tried everything but nothing resets all system files. Is there any way I can reset everything, like all system file?
This may  wipe all user data!!!

So make a backup just in case!!!!

You need to flash your appropriate firmware package of your device, download it here:

http://forum.xda-developers.com/showthread.php?t=2568853

Download Odin (google it)
Open Odin (duh)

Reboot your phone to download mode.(google it if you don't know how to)

Connect your phone to the computer

Put the firmware package in PDA/AP

Klik start to begin and your phone will reboot with "new system files"

Hope my answer helped.