Can DE2-115 handle more than 3.3V on its GPIO
The absolute maximum voltage permitted for Cyclone IV devices is 4.2V, but the recommended maximum operating input voltage is 3.6V. To ensure reliable operation you should reduce your signal voltages to 3.6V or less. 

If you don't need high speed and/or the drivers are strong enough then you might get away with passive resistor dividers (eg. 33 Ohms in series followed by 150 Ohms to ground). Otherwise you should use level shifting buffers such as 74HC4050 or 74LVXC3245.