Are these correct? What do they mean?

1. I need to change lanes. (Move from one lane to another lane. I know this is correct.)
2. I need to change lane. (What does this mean?)

How come Cambridge uses 'change gear' and not 'change gears' ?
3. I need to change gears. (Move from one gear to another gear.)
4. I need to change gear. (What does this mean?)

How come 'change scene' is not 'change scenes'?
5. She needed a change of scene. (What does this mean?)
6. She needed a change of scenes. (Change from one scene to another scene?)

How come Cambridge uses 'change hands' ? I know this is correct but how come it is not 'change hand' like the ones above. The ones above are singular but this one is not?
Hello Jack

In BrE:

#2 means the same as #1.

#4 is more usual than #3 (I don't think I've heard #3).

#5 is different because it consists of [noun + noun], rather than [infinitive + noun]. The singular 'of scene' denotes 'scene' in general, rather than a particular scene. ('Scene' here stands for 'environment': she wanted to be somewhere else.)

I'm not sure about 'change hands'. Will have to think about this one...