England open their Euro 2016 campaign against Russia in Marseille on Saturday having claimed three wins from three in pre-tournament warm-ups.
Captain Rooney started in England's final friendly against Portugal in an attacking trio with Harry Kane and Jamie Vardy.
However, England struggled to break down 10-man Portugal before Chris Smalling's 86th-minute header clinched victory.
With Rooney scoring just eight Premier League goals this season, his place in the side has come under scrutiny but the 30-year-old - who has adapted to a role in midfield for Manchester United in recent times - still has great confidence in his abilities.
"I think everyone who watches the game is entitled to their opinions, I know the qualities I have and I don't think I have to sit here and defend myself," Rooney said.
"I have played this game for a lot of years and I am aware my game has changed over years, in my opinion for the better.
"I changed my game slightly. I've seen players do that over years, who have played in a different way to what they did and became better players, it's natural for a footballer.
"Over last few months at Man U I've played midfield, it's a natural way of football, it happens. I always feel with my football intelligence I can play there and further my career there as well."
On England's prospects at the tournament, he added: "There is a real buzz around the place and everyone is excited, it is important performance levels match.
"We've got a talented squad capable of big things, but tournament football is different. It will be a challenge for us as a squad but we're confident we can do well."