Rafael Benitez took charge of Newcastle United last Friday.
Benitez took over from McClaren last Friday, and he has only had a limited amount of time to work with Newcastle’s squad.
The Spaniard has conducted just four training sessions so far, but Lascelles has already spotted differences between his and McClaren’s regimes.
"He's done a bit more tactical shape in training which the boys have taken on excellently," the centre back said.
Benitez took charge of his first Newcastle match on Monday evening, when he took his side to the King Power Stadium to face Leicester City.
Although Newcastle were beaten 1-0, their performance in the contest was encouraging.
Benitez now has another nine games to save the Tynesiders from relegation, with Sunderland next up.
If Newcastle do beat their local rivals, they will move ahead of them in the table, and Lascelles admits that only a win will be acceptable.
"I think the game on Sunday against Sunderland - we have to win that. We literally have to win,” the former Nottingham Forest man added. “I think we've not beaten them in seven games, but we've just got to go into that confident.”