Complex sentence: The fell's elevation seems to have reduced by two metres in recent years, the Ordnance Survey now give it a height of 661 m (2,168 ft) in the most recent map updates after having recorded it at 663 metres for many years.
Split into simpler sentences: The fell's elevation seems to have decreased by two metres in recent years. The Ordnance Survey now give it a height of 661 m (2,168 ft) in the most recent map updates after having recorded it at 663 metres for many years.