Blues are set to reveal their retained squad list in the week after Saturday's final game of the season.
"It's not an easy week but it's part of the moving forward process," 42-year-old Rowett told BBC WM 95.6.
"I've got to do it with a critical eye and a semi-ruthless mentality."
Rowett has seven players out of contract in the summer and must also make a decision on whether to agree deals for a number of loan players, including Derby defender Ryan Shotton.
"My job is to make the team better and garner some success," Rowett said. "Most of the decisions are pretty self-explanatory. The players that have been on loan with us for a vast period, they and us potentially see their future elsewhere.
"The players that are currently here and out of contract will be the first to know what decision we make."
Shotton, who has been with Blues since January, is one player who is giving Rowett food for thought.
"He's surprised me a little bit in some ways," Rowett said. "He's got a real desire to be a part of what we're doing and I genuinely believe he sees this a chance to kick-start his career.
"He needs to nail down that centre-half slot somewhere and we would have an interest in trying to keep him, but he's not our player and we don't know whether Derby see him in their plans or would want a huge fee for him."
Birmingham will secure a ninth-place finish in the Championship table if they can better Brentford's result at Huddersfield when they travel to Cardiff on Saturday.
Birmingham City boss Gary Rowett says he will have to be a bit "ruthless" when it comes to deciding which players stay at the Championship club next season and which players will leave.