La albañil dice que la baldosa y el azulejo se pueden cambiar en una mañana.

Because albañil is a common-gender noun in Spanish. That means the noun itself usually stays the same, and the article shows whether the person is male or female:

• el albañil = the male builder / bricklayer
• la albañil = the female builder / bricklayer

This is normal for many profession nouns in Spanish. Unlike some other job words, albañil does not usually change to albañila in standard usage.

Albañil usually means a builder, bricklayer, or construction worker, especially someone who works with walls, plaster, tiles, cement, and similar materials.

In this sentence, that makes sense because the person is talking about changing a baldosa and an azulejo, both of which are kinds of tile.

In Spain, these words are related but not identical:

• baldosa usually means a tile, especially a floor tile
• azulejo usually means a ceramic wall tile, often the kind used in kitchens or bathrooms

So the sentence mentions two different kinds of tile. Depending on context, the distinction may matter:

• baldosa → more associated with floors
• azulejo → more associated with walls

Because Spanish often uses the singular to refer to each item as a type or individual unit.

Here, la baldosa y el azulejo means something like:

• the tile and the wall tile
• or the floor tile and the wall tile

Even though the two nouns are singular individually, together they form a compound subject, so the verb later becomes plural: se pueden cambiar.

Because the subject is plural overall:

• la baldosa y el azulejo = two things together

So the verb must agree in the plural:

• se pueden cambiar = can be changed

If there were only one thing, you would use the singular:

• La baldosa se puede cambiar.

Here se is not really reflexive in the sense of someone changes themselves. Instead, it is part of a very common Spanish structure often called passive se.

So:

• se pueden cambiar = can be changed

Literally, Spanish builds it as something like:

• the tile and the wall tile change themselves but that is not how it is understood.

The real meaning is passive:

• they can be changed

This structure is extremely common in Spanish instead of using a full passive with ser:

• La baldosa y el azulejo pueden ser cambiados This is grammatical, but se pueden cambiar sounds much more natural.

Because que introduces the clause that reports what the person says.

• dice que... = says that...

So the structure is:

• La albañil dice = The builder says
• que la baldosa y el azulejo se pueden cambiar en una mañana = that the tile and the wall tile can be changed in one morning

In Spanish, after verbs like decir, pensar, creer, saber, and many others, que is very often required.

Spanish uses definite articles more often than English does. Here, la and el can help present these nouns as known items, specific elements in the situation, or categories being discussed.

So Spanish often sounds natural with:

• la baldosa y el azulejo

where English might prefer:

• the tile and the wall tile
• or sometimes just tile and wall tile, depending on context

Repeating the article before each noun is also normal when two nouns are linked by y.

Because the basic verb here is cambiar = to change / to replace.

In se pueden cambiar, the se belongs to the passive construction, not to the infinitive itself. So the verb stays as cambiar.

Compare:

• Se pueden cambiar. = They can be changed.
• Pueden cambiarse. = They can be changed.

Both are possible, but in your sentence the se is placed before the conjugated verb pueden, which is very common.

En una mañana means in one morning or within the space of a morning.

It suggests the job can be completed during that amount of time.

Here en expresses the time needed to complete something:

• Lo hago en una hora. = I do it in an hour.
• Se puede cambiar en una mañana. = It can be changed in one morning.

It does not mean simply during the morning in a loose sense; it emphasizes that the work fits into that time span.

Yes. Once la baldosa y el azulejo are taken together, they become plural as a group, so English would naturally refer to them as they:

• They can be changed in one morning.

That is why Spanish uses pueden and not puede.

Yes, dice is the present tense of decir.

• dice = says
• depending on context, it can sometimes also be translated as is saying

In most basic translations, says is the best choice:

• The female builder says that...

Yes, it is grammatically natural. A speaker from Spain would understand it perfectly.

A few notes:

• albañil is very normal in Spain
• the distinction between baldosa and azulejo is especially familiar in Spain
• se pueden cambiar is a very natural Spanish way to say can be changed

If anything, in real conversation a speaker might choose slightly different wording depending on whether they mean a specific floor tile and wall tile, or tiles in general, but the sentence itself is completely fine.