Baggage with measurements exceeding 178 cm (width + length + height) is normally considered as bulky luggage.
To register bulky luggage, first go to the ordinary check-in counter for your flight. After checking in you will be directed to the special bulky baggage counter.
If you have already checked in for your flight via the Internet, go to the specially marked "Baggage Drop-off" counter, which is near the ordinary check-in counters. There you will next be directed to the bulky baggage counter.
For further information about the maximum dimensions for bulky baggage and possible additional charges for its conveyance, consult your airline directly.