Complex sentence: In the 1840s the 1st Baron Mostyn commissioned architect Ambrose Poynter to remodel the house, which was carried out mainly in 1846--47 in a Jacobean style inspired by the pre-existing building.
Split into simpler sentences: In the 1840s the 1st Baron Mostyn commissioned Ambrose Poynter to remodel the existing house. This was carried out mainly in 1846--47 in Jacobean style, this being inspired by the pre-existing building.