to switch gears, to shift gears
are often (too often for my taste, but that is a different matter) used to announce a switch from one topic to another in an oral presentation (e.g., a scientific talk).
As far as vehicles are concerned, gears are switched to change speed, not direction. Hence, I would rather associate a "switch of gears" with a change in the speed of the presentation. Therefore, expressions such as "to change lanes" or "to change direction" seem to be more appropriate.
Does anyone have knowledge about the origin of the phrase? I could not find it in the respectable dictionaries, so I'm also not sure how common it really is.
(Another interesting point is that the phrase seems to be particularly popular in the United States, despite the dominance of automatic cars.)