ok what model is the mehran.
as said by zulfiqar bhai... keep your car on level ground. and remove the lower pipe of the radiator in your car.
the upper pipe where the pipe goes into the engine block. normaly thats where the thermostat valve is. you will need to remove the thermostat valve and put all the hoses back. then fill with clean water. run the engine a little. then drain the water again. do this a few times to get the loose rust out.
the proper way would be to put in radiator cleaner. but i guess you can leave it for now if your car isnt heating up.
once all the rust is out.
connect all pipes and fill with pre mixed coolant. you can buy zic coolant. i think 5 liter for around 1350 rs. order from zic oil website they will bring it to your home. half fill the coolant and run the engine.
then replace the thermostat valve and completely fill the coolant. you will need around 3 liters