I really don't know which brands are available in Pakistan.
Auto makers do recommend you flush out the coolant and add new coolant after 160,000 miles ( 250,000). Thats if your car has long life coolant (orange color). Recommanded flush period for ethylene glycol-base (green) coolant is 100,000 km (160,000 km). It is also recommended that you change the thermostat and radiator cap every time you flush the coolant.
If you are short on money... I'd say forget flushing.. it's not a big deal. Most people don't flush out the coolant ever. As long as you keep adding fresh coolant to top up.. You are going to be just fine..