Complex sentence: Yoon Eun Hye replaced Lee G in the lineup and the group's first single from the album' Get Up' was soon popular nationwide and for the first time, they reached the number one spot on the Korean music pop charts.
Split into simpler sentences: Yoon Eun Hye replaced Lee Gai in the lineup and the group's first single from the album "Get Up" was soon popular nationwide. For the first time, they reached the number one spot on the Korean music pop charts.