I uploaded a map into the /client/ and uploaded car_jump_arena.zip and changed the settings to /levels/car_jump_arena/info.json but it does not run.

How to fix?

Go to settings then look at the top you see config or settings cfg open that look for where you see /levels and ensure you take the spacing out also try to open the file and see what the folder on the inside is called might be named something different and thats what the folder will actually read