HelloCustomerand welcome to JA,
Do you see any coolant leaks like by the hoses or radiator or waterpump ? After replacing the themostat, you need to bleed the system. There is a special way to do it. Fill up your coolant system , run your engine warm with the heat on . On the radiator close to the fill cap ther is a plastic screw which you need to open to beed the system. leave the screw open until coolant comes out then close it and your system should be ok.
Does your car still overheats ? If so there can be three things wrong here, first the waterpump doesn't work right, to check this remove top radiator hose and start car briefly and see if the coolant will be thrown out there, if it does it means that your waterpump is circulating the coolant which is good, second the clutch fan off the fan is bad to check this is to have the car warmed up and see if the fan turns quickly if you rev the engine up it should rev up too. if this is not the case then only rest is a blown headgasket , which is a costly repair. I hope not for you . Good luck