Thanks Paresh, for posing this question!
First and foremost, we cannot, per say, stop people from being judgmental unless we know them and we explain why not to be judgmental and how not to be. Even if we succeed once in convincing people not to be so, that can remain to be the one time or the only time unless people decide from within not to be judgmental.
Now, how to stop being judgmental?
Being judgmental comes from a basic fact that we are not open for different perspectives, rather different facts that we do not know while looking at a particular thing. Widening the perspectives is one thing that can be of great help which makes us to be open to accept the fact that 'what we are seeing or perceiving might be something out of much, and there can exist something else too'. Also, it allows us to think that 'the other person might be coming from a different perspective altogether'. The moment our thinking allows us to look for above said, for sure we take time before being deciding upon anything; and this time gap is sufficient to stop us from being judgmental, I guess. The moment we are consciously looking for another perspective is the moment we not being judgmental. It helps a lot actually, to an individual and to society, if all of us can practice not to be judgmental.