Complex sentence: Her original engines were derated as a high service speed was no longer needed, at the same time the exterior of the ship was repainted in all white and her passenger capacity was also reduced to only 500 first-class passengers.
Split into simpler sentences: Her original engines were derated as a high service speed was no longer needed. At the same time, the exterior of the ship was repainted in all white and her passenger capacity was also reduced to only 500 first-class passengers.