change gear BrE
shift gears AmE
switch gears AmE

With those few words, she had shifted gears on my thinking.

He considered that, and I could almost see him shift gears.

Then, quickly, she shifted gears to the heart of her game.

She caught my arm as I started to shift gears for the turn.

These guys could shift gears so quickly that it was hard to keep up with them.

She could actually sense him shifting gears at the sound of a female voice.

I tried to shift mental gears, to keep up with the change in subject.

It is my generation that has had to shift gears.

In his late work he is clearly trying to shift gears, though with mixed success.

Mike, of course, shifted mental gears in something under a second.