He owns a mansion on Kensington Palace Gardens, which he bought, in 2004, for forty-one million pounds. Since renovated, it has thirteen bedrooms, a cinema, an indoor-outdoor swimming pool, and armored-glass windows.
Is this "since" an adverb, like this?
It was since renovated and now it has thirteen bedroom?
Yes, "it has since been renovated", "it has been renovated since he bought it in 2004".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.