What action does "replace" refer to?

The term "replace" specifically refers to the action of substituting one item for another. In practical usage, when something is replaced, it means that the original item or element is taken out and a different one is put in its place. For example, if a broken light bulb is replaced by a new one, the old bulb is removed, and the new bulb is installed to serve the same function.

In contrast, changing one position for another implies a switch of roles or locations, which does not capture the essence of substitution inherent in "replace." Similarly, increasing the volume of something pertains to amplification and does not relate to the concept of substituting items. Lastly, adopting a new method indicates a change in procedure or approach, rather than an item being swapped for another. Thus, "substituting one item for another" accurately describes the core action associated with the word "replace."