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.
With the transfer window closed he has a tough task to reinvigorate Roma, who finished sixth last term having been runners-up and Italian Cup winners in 2007 and 2008.
"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."
BAD RESULTS
Ranieri led Juve to third spot in 2008 in their first campaign back in Serie A after being demoted for match-fixing but was replaced by Ciro Ferrara towards the end of last season after a run of bad results.
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.
Ranieri joins a club in turmoil with Roma fans continually protesting against president Rosella Sensi over what they see as her lack of spending power.
Two takeover bids have failed and Italy midfielder Alberto Aquilani was sold to Liverpool in the close season with no major signings arriving.
The club's share price was down three percent on Wednesday.
