Hi Natasa,
Loosing 6 kg of weight in one month is really not possible and of course its unhealthy. To loose weight you diet plays an important role so as to take in less calories but you need to also burn calories by doing exercises so as to reduce weight more better way. You need to include both types of exercises like cardio and weight training exercises for better results. Cardio exercises includes activities like brisk walking, jogging, running, swimming, skipping, etc. while weight training exercises includes lunges, squats, push ups, pull over ,etc. We need to have a combination of both types of exercises and do it for atleast 45 min for better results.