In my house all heating ducts working fine except 2 upstair rooms.I have gas furnace.In the kids upstair rooms from the heating ducts just lightly heated air coming out while all the outlets on ground floor has hot air coming.Also upstair bathroom having good hot air coming out.Why 2 rooms doesnot have hot air coming out.I have no zones just one thermostat controls the whole house.

Your system need to have a air balance done to make sure each room gets the proper air flow for its size.

Some systems have air dampers built into the duct with a small handle to turn but without a air volume monitor of some type it will be difficult to adjust correctly.