I have mercedes benz 230 kompreser 4 doors i want to change the rims from 17" to 16" what will this effect tge car?

yes and no....It will make bigger wheels with the same size tires would cause rubbing and loss of performance however if you take the wheel size up and change the tires accordingly the only thing it will effect is how it looks

The problem im facing is tht im always having flat tyres becaues of my 17" wheels so if u can help me nd tell me if i installed 16 " tyres whats the perfect size of wheels to install?

To get the same ratio, so your gear ratios stay the same as the engineers intended and your speedometer reads accurately, a 16" tire would have to have a profile one inch taller than the tire on the 17" wheel. As for your question it would have to be a 16" wheel as only that would fit a 16" tire, the 16 is the diameter of the inside of the tire bead to bead, the profile is the distance from the bead to the tread. Needs to be "taller"

I am curious. Why do you think the flat tires are because they are 17"?

Another thing to consider: make sure your brakes will fit in the smaller wheels. I agree with the above... I don't think smaller wheels will prevent you from getting flats.