Complex sentence: The Social-National Party of Ukraine changed its name to the All-Ukrainian Union "Svoboda" in February 2004 with the arrival of Oleh Tyahnybok as party leader, who made significant efforts to moderate the party's extremist image.
Split into simpler sentences: The Social-National Party of Ukraine changed its name to the All-Ukrainian Union "Svoboda" in February 2004 with the arrival of Oleh Tyahnybok as party leader. Tyahnybok made significant efforts to moderate the party's extremist image.