The 57-year-old agreed a two-year deal on Tuesday to replace Luciano Spalletti, who quit after the club lost their opening two Serie A games of the season and struggled to reinforce their squad in the transfer market.
"They certainly need a shock because this team needs to react immediately. Maybe the lads have lost a bit of conviction," Rome-born Ranieri told a news conference on Wednesday.
"In the last four years (under Spalletti) this team has done great things, playing some of the most beautiful football in Europe," added former Juventus and Chelsea coach Ranieri.
"I was proud as a Roman to see them play. I can say I'm coming home with a huge desire to do well."
He acknowledged his style of play might not be as eye-catching as Spalletti's but was unperturbed by captain Francesco Totti being a dominant figure at the club.
"My philosophy is a little different to Spalletti's, I will bring my pragmatism to this team. I expect Totti to just be Totti," said Ranieri, who occasionally clashed with Juve captain Alessandro Del Piero during his two years in Turin.
The club's share price was down three percent on Wednesday.
