First of all, you have to feel certain that the overheating isn't caused by something amiss in the hydraulic system operation that puts excessive load on engine. If you're confident that the hydro system is working proper, then you can assume it's an engine related problem. As gramps said, make sure the radiator is clean externally.
Once you've done that, the next thing would be to check thermostat operation. You can either remove the thermostat and heat it in a pot of water while checking temperature of the water to see if it operates proper, or you can remove the radiator cap, block the radiator with some cardboard or similar material to restrict cooling air, then start/run engine. As the temperature of the engine coolant rises, you should see coolant start to flow through the radiator when temp gauge is at proper operating temperature.
If you notice proper coolant flow at operating temperature, then it's possible the radiator is clogged internally and would require taking to a radiator shop to be disassembled and cleaned or re-cored. I hope this helps.