Is 'used to' describing something changed?

Unfortunately, the English language can be confusing, even more so than other languages.

"Used to" can, like you said, be used to explain something that's been changed--for example:

I used to like broccoli, but I don't anymore.

I used to like only broccoli, but now I like asparagus, as well.

I used to be afraid of snakes, but now I'm not.

I used to be afraid of snakes, but now I won't even be in the same city with one.

If you leave out the part after the comma, it generally means "but not anymore". So:

I used to be afraid of snakes. [but not anymore]

Someone may misunderstand you in this case.

You can also put emphasis on the word "used" to help someone understand the new meaning.

I used to be afraid of snakes.

Good luck!

Your example sentence strongly suggests that I am no longer afraid of snakes. But it doesn't imply it unequivocally. For example, one might say

I used to be afraid of snakes; but now, in addition to snakes, I'm also afraid of spiders, scorpions and rabbits.

Used to is an idiom that has a very special presupposition and some unusual properties.

First, it's always pronounced /yustə/ or /yustu/, never /yuzd tu/:

• I used to be afraid of snakes. /ay 'yustəbiyə fredə 'sneks/ [NOT /'yuzd/]

Second, English has two idioms pronounced this way -- one, which always appears as a predicate adjective with some form of be -- means 'accustomed to'. That's not the one under discussion here.

• I am used to driving in the left lane.

Third, the particular used to idiom under discussion here can appear in any sentence, with the main verb (in infinitive form) following it:

• He came/comes here often. ~ He used to come here often.
• Carter is/was President. ~ Carter used to be President.

(Since infinitives have no tense, they can refer to either a present or past tense verb.)

Fourth, these used to constructions refer to both present and past tense sentences simultaneously. However, they don't refer in the same way; the past is asserted (i.e, claimed by the speaker to be true), while the present is presupposed (i.e, assumed by the speaker -- and normally the listener as well -- to be true).

That is, if one says that Carter used to be President, then one is saying that

• the past sentence Carter was President is True

and also presupposing that

• the present sentence Carter is President is False.

And if you did say that, and then someone said "You're wrong!", what would they be denying? One can only deny an assertion, so they'd have to mean that Carter was never President. They couldn't possibly mean that Carter is still President.

This can work both ways -- if you said, instead,

• Carter isn't President any more.

and someone said you were wrong, they'd have to be denying that he was not President now.

One more reason why there are usually several different ways to say things.