alter
v.v. to change something slightly. You use this when you want to say that the basic thing is the same, but some parts are now different.
v. to make a partial change in character, appearance, or composition without transforming the object into something else entirely. Transitive in most contexts, though it can function intransitively to describe a process of change.
I need to alter my plans for the weekend.
The tailor had to alter the jacket slightly so that it would fit more comfortably around the shoulders.
Psychologists have found that even minor changes in environment can significantly alter a person's mood and cognitive performance over a long period of time.
From Old French alterer (French altérer), from Medieval Latin alterāre (“to make other”), from Latin alter (“the other”), from al- (seen in alius (“other”), alienus (“of another”), etc.; see alias, alien, etc.) + compar. suffix -ter.
Probably from alter ego.
The verb is transitive and takes a direct object. It is often used in formal or academic contexts where 'change' might feel too general.
The weather altered into rainThe weather changed to rainAlter implies a modification of an existing thing rather than a total transition from one state to another.