。
She sang better than him.
Literal
She [topic-は] him [than-より] skillfully sang.
より is the standard comparative particle, 'than.' The compared standard (彼) takes より, and the comparative is left implicit — Japanese doesn't add a 'more' word; the comparison is encoded by より alone. 上手に is the adverbial form of 上手 (じょうず, a na-adjective, 'skilled, good at'), modifying the verb. Note that 上手 itself doesn't intensify in the comparative; the entire comparison sits in 彼より.