Ar trebui să schimb rezervarea, pentru că ajungem mai târziu.

Ar trebui să means should or ought to.

It is a very common Romanian way to give advice or say what would be appropriate.

• ar trebui = literally something like it would be necessary / it would be proper
• să = introduces the following verb

So:

• Ar trebui să schimb rezervarea = I should change the reservation

This structure is followed by a verb in the subjunctive:

• Ar trebui să plec = I should leave
• Ar trebui să sun = I should call

Because schimb is the 1st person singular present form of a schimba (to change).

So:

• a schimba = to change
• schimb = I change

After ar trebui să, Romanian normally uses a conjugated verb, not the infinitive.

Compare:

• Trebuie să plec = I have to leave
• Ar trebui să schimb rezervarea = I should change the reservation

English uses to change, but Romanian does not use the infinitive here.

Să is a very important Romanian word used to introduce the subjunctive.

In this sentence, ar trebui să schimb uses the subjunctive pattern. English does not always show this clearly, so it can feel unusual to learners.

You will often see să after verbs and expressions like:

• vreau să merg = I want to go
• pot să vin = I can come
• trebuie să plec = I must leave
• ar trebui să schimb = I should change

So the short answer is: să is required by this construction.

Because rezervarea means the reservation.

Romanian usually attaches the definite article to the end of the noun:

• rezervare = reservation
• rezervarea = the reservation

So:

• schimb rezervarea = I change the reservation
• schimb o rezervare = I change a reservation

This attached article is very common in Romanian:

• hotel = hotel

• hotelul = the hotel

• masă = table
• masa = the table

Ajungem means we arrive.

The ending -em shows 1st person plural.

So the sentence means that we are arriving later, even though the speaker says I should change the reservation.

That combination makes sense in English too:

• I should change the reservation because we’re arriving later.

The speaker is the person who will make the change, but the arrival concerns a group.

Other forms of a ajunge:

• ajung = I arrive
• ajungi = you arrive
• ajunge = he/she arrives
• ajungem = we arrive
• ajungeți = you all arrive
• ajung = they arrive

Mai târziu means later.

• târziu = late
• mai târziu = later

Examples:

• Vin târziu = I’m coming late
• Vin mai târziu = I’m coming later

In your sentence:

• ajungem mai târziu = we are arriving later

Depending on context, English might also say we’ll arrive later than expected.

Yes. Pentru că means because.

It introduces the reason:

• Ar trebui să schimb rezervarea = I should change the reservation
• pentru că ajungem mai târziu = because we’re arriving later

A useful note: că is a very common connector in Romanian and often means that in other contexts, but in pentru că, the whole phrase means because.

Example:

• Nu vin pentru că sunt obosit = I’m not coming because I’m tired

Because Romanian usually puts the definite article at the end of the noun instead of using a separate word like English the.

So English says:

• the reservation

Romanian says:

• rezervarea

This is one of the major structural differences between English and Romanian.

A few more examples:

• carte = book

• cartea = the book

• camera can mean the room
• o cameră = a room

So rezervarea is perfectly normal Romanian structure.

Yes — Ar trebui să schimb rezervarea is usually weaker, softer, and more like advice or a reasonable decision.

• Ar trebui să schimb rezervarea = I should change the reservation
• Trebuie să schimb rezervarea = I must / have to change the reservation

So ar trebui să often sounds less absolute than trebuie să.

That distinction is very useful in Romanian:

• Trebuie să plec = I have to leave
• Ar trebui să plec = I should leave

Yes, Romanian word order is somewhat flexible, but the given order is the most natural and neutral.

Normal version:

• Ar trebui să schimb rezervarea, pentru că ajungem mai târziu.

You might also hear variations for emphasis, such as:

• Pentru că ajungem mai târziu, ar trebui să schimb rezervarea.

That puts more focus on the reason first:

• Because we’re arriving later, I should change the reservation.

So the original sentence is standard and natural, but Romanian can move parts around more freely than English in some cases.

Yes. Romanian present tense often covers meanings that English expresses with either the simple present or the present progressive, depending on context.

So:

• ajungem literally = we arrive
• in context, it can naturally mean we’re arriving

That is why the sentence can be translated idiomatically as:

• I should change the reservation, because we’re arriving later.

Romanian often relies on context where English chooses between:

• we arrive
• we are arriving
• sometimes even we will arrive

A rough English-friendly pronunciation guide would be:

Ar truh-BWEE suh skimb reh-zehr-vah-REE-ah, pen-troo kuh ah-ZHOON-zhem mye TUR-zyee-oo

A few helpful pronunciation notes:

• ă is a short central vowel, something like a very reduced uh
• â / î is a deeper central vowel, not exactly like any standard English vowel
• sch in schimb sounds like sk here
• j in ajungem sounds like the s in measure
• târziu may be tricky; the final part is roughly zyee-oo

You do not need perfect pronunciation immediately, but it helps to notice that Romanian spelling is fairly consistent compared with English.

Yes, possibly, but the nuance changes a little.

• a schimba = to change, switch, alter
• a modifica = to modify, alter

In the context of a booking, a schimba rezervarea is very natural and common, especially if you mean changing the details or rebooking in some way.

A modifica rezervarea is also understandable and can sound slightly more formal or administrative.

So for everyday Romanian, schimb rezervarea is a very good choice.