Since you're in Korea with a phone i'm assuming you know enough Korean to navigate and sign up for this site.
Search for your model number: M250L
There's only been one firmware dump (the original) to my knowledge since this particular model isn't very popular. Use an insecure kernel to root first then flash the original kernel back when you've finished rooting.
You can find the original kernel on matpclub and an insecure kernel either here or on matpclub. Check the 'Development' subforum for more information.