La graduación cambió mucho.

In Spanish, nouns are very often used with a definite article where English might leave it out.

So la graduación literally looks like the graduation, but in Spanish that can still refer to the event in a general, natural way.

Compare:

• La graduación fue ayer. = Graduation was yesterday.
• Me gustó la graduación. = I liked the graduation ceremony.

Using la here is completely normal.

Yes, graduación is feminine, which is why it takes la.

A helpful clue is the ending -ción. Nouns ending in -ción are almost always feminine:

• la canción
• la situación
• la educación
• la graduación

So if you see -ción, feminine is a very safe guess.

Cambió is the preterite form of cambiar, meaning changed.

• cambia = changes / is changing
• cambió = changed

So:

• La graduación cambia mucho = Graduation changes a lot / is changing a lot
• La graduación cambió mucho = The graduation changed a lot

The sentence uses a completed past action or change, so cambió is the right form.

The accent mark shows both pronunciation and meaning.

• cambio = I change or change as a noun
• cambió = he/she/it changed

Without the accent, it would be a different word.

Pronunciation:

• cam-bio → stress on cam
• cam-bió → stress on bió

That written accent is important because it tells you this is the third-person singular preterite form.

Here, mucho means a lot or a great deal.

Since it modifies the verb cambió, it works like an adverb:

• cambió mucho = changed a lot

This is different from mucho/a/os/as used as an adjective before a noun:

• mucha gente = a lot of people
• muchos cambios = many changes

But after a verb, as in this sentence, mucho stays in the basic form:

• trabaja mucho
• llueve mucho
• cambió mucho

In Spanish, adverbs like mucho usually come after the verb.

So:

• cambió mucho
• habla mucho
• me gusta mucho

That is the normal word order. English often does the same with a lot:

• It changed a lot

So this part is actually quite close to English.

No, nothing is missing grammatically.

La graduación is the subject, and cambió is an intransitive use of cambiar here, meaning underwent change or became different.

So the structure is:

• La graduación = subject
• cambió = verb
• mucho = adverb

Spanish does not need to add something like itself or an object here.

Compare:

• La ciudad cambió mucho. = The city changed a lot.
• Mi vida cambió mucho. = My life changed a lot.

Same pattern.

Yes, that is also possible, but the nuance is a little different.

• La graduación cambió mucho → simple past; it changed a lot
• La graduación ha cambiado mucho → present perfect; it has changed a lot

In Spain, the present perfect is especially common when the change is connected to the present or to a recent time period. The preterite often sounds more like a completed past event, seen as a whole.

So both are correct, but they do not always feel exactly the same.

Not always. Depending on context, graduación can have other meanings too, such as:

• graduation / graduation ceremony
• gradation
• strength/prescription of glasses or lenses in some contexts

For example:

• la graduación de la universidad = the graduation ceremony
• la graduación de las gafas = the glasses prescription

In your sentence, the intended meaning is clear from context, but it is useful to know the word can be broader than English graduation.

A simple pronunciation guide is:

la gra-dua-CIÓN cam-BIÓ MU-cho

More approximately for an English speaker:

lah grah-dwah-see-ON kahm-BYOH MOO-cho

Notes:

• ción sounds roughly like syon
• ió in cambió is one syllable, with the stress there
• ch in mucho is like English ch

So the main stressed syllables are:

• graduaCIÓN
• camBIÓ
• MUcho

Normally, no. That would sound unnatural in standard Spanish.

Spanish generally wants the article here:

• La graduación cambió mucho.

Leaving out the article is much less common than in English. English often says Graduation changed a lot, but Spanish usually prefers La graduación... in a sentence like this.