Carvalho said his team could not afford to sit on the 1-0 lead they have from Saturday's first leg when they travel to Bosnia on Wednesday.
"It's important not to start by playing in defence, we have to play our football and try to score," Carvalho said.
"When we have the ball we will try to attack from the first minute, but if we get to 80 minutes and it is 0-0, we also know that at that moment the important thing will be to defend well."
A header by Bruno Alves gave Portugal a 1-0 win in Lisbon and although they missed a host of chances they were also let off when Bosnia hit the woodwork twice in the final minute.
Portugal will again miss the injured Cristiano Ronaldo in Zenica, where coach Carlos Queiroz said a poor pitch, snow and a fervent Bosnian crowd would present further challenges.
"How do we counter that atmosphere? (By) trying to keep the ball and playing, always being dangerous," said Carvalho.
"They (Bosnia) have a lot of hope, but so do we, and if we have the ball we will gain confidence because it is also not easy to play against us and if we score a goal the situation gets complicated for them."
