Poyet was taking charge of his first match with the Black Cats, and said that he will assess his players thoroughly, after only having the chance to work with them since they returned from international duty earlier this week.
"We need to change things and we are only going to do that with hard work and by winning football matches," Poyet told Sky Sports News.
"It sounds easy, but we are going to have to start winning football matches. We will analyse the players, technically, tactically and mentally. We have problems that we need to address.
"We need to be stronger mentally, not just the players, but everyone at the club."
Sunderland are bottom of the Premier League.