s3 modified

[amal dev]

I tried to update my Samsung S3 GT-19300 phone but I got a msg dat my phone is modified so no updates r possible ...
Device status is showing CUSTOM ..
N I don't have an external sd card also as I have nly the inbuilt 16gb ..
So unmounting it is not an option ..
I have never rooted d phone also
Any solutions ??...