How much should you walk every day to lose 4 kilos?

Walk as much or as little as you like. Walking is not quite strenuous enough for you to loose weight unless you never walk or you are obese.

Eat less, what you do eat - chew well - and drink lots of water.

Do physical activity that makes you sweat for 20 minutes at least 3 times a week preferably every day.

In a few weeks you will have lost those kilos.