Holding the shout key for a longer time will let you perform a higher-level Dragon Shout.
Please note though, that there are some bugs with this quest:
You might experience a minor bug where the objective "Speak to Arngeir" does not register as complete. If you have spoken to Arngeir, make sure you exit out of the small door down the stairs in front of Arngeir out into Skyrim. Sometimes when you turn around and exit out the big double doors, it will not register as completed. This can be easily fixed by re-entering the building and using the other exit (some players report this does not work either).
Also, you should make sure your shout power is ready to use (not used that day) before entering the building and talking to Arngeir. Using the wait feature to go to the next day then shouting at Arngeir does not work, it is unknown if this permanently makes this quest incomplete.
— Wikia - Elder Scrolls V: Skyrim - The Way of the Voice