By 'reset' you mean reboot or doing a factory reset? If it's the first, just hold the power and home button together for about 5 seconds. The device will reboot itself.
If you want to factory reset, you can power off the device (just hold the power button until it shuts off or remove the battery). Then, to power up, press and hold the Power button + Volume Up button until your device enters Recovery mode. Here you'll get the option to wipe your device, bringing it back to factory-default state. Just remember that doing this will also delete ALL DATA in your phone, so whatever is stored there (pictures, documents, apps, configuration files, etc.) will be lost.