Cambio la federa del cuscino e stendo il copriletto nuovo sul letto.

Cambio is the 1st person singular present indicative of cambiare.

So:

• io cambio = I change / I am changing
• cambio on its own already means I change, because the verb ending -o shows the subject.

In the same sentence, stendo is also 1st person singular present indicative, from stendere.

So the sentence has two verbs with the same subject:

• cambio = I change
• stendo = I spread / I lay out

Italian often drops subject pronouns when they are not needed. The verb ending usually makes the subject clear.

• cambio already tells you the subject is I
• stendo also already tells you the subject is I

So Io cambio la federa... is possible, but it would usually sound more emphatic, like:

• Io cambio la federa, non tu. = I’m changing the pillowcase, not you.

In a neutral sentence, leaving out io is the most natural choice.

It can mean either one, depending on context.

Italian present tense often covers both:

• I change / I spread
• I am changing / I am spreading

So Cambio la federa del cuscino e stendo il copriletto nuovo sul letto could describe:

1. a routine or habitual action, or
2. something happening right now

If you want to stress that it is happening right now, Italian often uses stare + gerundio:

• Sto cambiando la federa del cuscino e sto stendendo il copriletto nuovo sul letto.

But the simple present is very common and natural.

Yes, but in this context cambio is best understood as I change / replace.

With household items, cambiare often means:

• remove the old one
• put on a new or clean one

So cambio la federa del cuscino means something like:

• I change the pillowcase
• I replace the pillowcase
• I put a fresh pillowcase on

English also says change the sheets, so this use is very similar.

Because federa means pillowcase, and Italian often expresses this relationship with di.

• federa = pillowcase
• cuscino = pillow
• del = di + il = of the

So literally:

• la federa del cuscino = the pillowcase of the pillow

In natural English, we say the pillowcase. In Italian, del cuscino helps specify what kind of cover it is.

This structure is very common:

• la porta della casa = the door of the house
• il colore del muro = the color of the wall

Because Italian uses definite articles much more often than English.

In English, we might say:

• I change the pillowcase and spread a new bedspread on the bed

In Italian, it is very normal to use articles with everyday objects that are understood in context:

• la federa
• del cuscino
• il copriletto
• sul letto

This does not usually sound overly specific in Italian. It is simply the normal pattern.

Stendo comes from stendere, which often means:

• to spread out
• to lay out
• to stretch out flat

In this sentence, stendo il copriletto nuovo sul letto means:

• I spread the new bedspread on the bed
• I lay the new bedspread out on the bed

It is a very natural verb for fabric, sheets, blankets, towels, and similar things.

For example:

• Stendo il lenzuolo sul materasso. = I spread the sheet on the mattress.
• Stendo i panni. = I hang out / spread out the laundry.

Because stendere is more specific than mettere.

• mettere = to put
• stendere = to spread out / lay flat

If you are placing fabric neatly over a surface, stendere is often the better choice.

So:

• metto il copriletto sul letto = I put the bedspread on the bed
• stendo il copriletto sul letto = I spread the bedspread out on the bed

Both can be possible, but stendo gives a more precise image.

In Italian, adjectives can often go after the noun, and that is the most neutral position here.

• il copriletto nuovo = the new bedspread

This usually means the bedspread is new in a straightforward, descriptive sense.

If you say:

• il nuovo copriletto

that can sound slightly more like:

• the new bedspread as opposed to the old one
• the newly chosen/replacement bedspread

So both are possible, but the nuance can shift a little.

Very roughly:

• copriletto nuovo = a bedspread that is new
• nuovo copriletto = the new bedspread, perhaps contrasted with another one

Sul is a contraction of:

• su + il = sul

So:

• sul letto = on the bed

This kind of contraction is very common in Italian:

• su + la = sulla
• su + i = sui
• di + il = del
• a + il = al

Since letto is masculine singular, it takes il, and that gives sul letto.

Sometimes yes, but sul letto is the more natural choice here.

• sul letto usually means on the bed, in contact with its surface
• sopra il letto can also mean above the bed, depending on context

Since the bedspread is being laid directly onto the bed, sul letto is clearer and more idiomatic.

So for this sentence, sul letto is the best option.

Because the subject is still the same, and Italian normally does not repeat it unless there is a reason to emphasize it.

So this is perfectly natural:

• Cambio la federa del cuscino e stendo il copriletto nuovo sul letto.

The subject I is understood for both verbs.

Repeating io would usually add emphasis or contrast, and would sound less neutral:

• Io cambio la federa del cuscino e io stendo il copriletto...

That is grammatically possible, but not the normal neutral style.

These are related but not the same:

• copriletto = bedspread / coverlet
  A cover that goes over the bed, often decorative or light.
• coperta = blanket
  Something used mainly for warmth.
• lenzuolo = sheet
  The fabric sheet on the bed.

So in this sentence, copriletto is specifically the outer bed covering being spread over the bed.

This is the most natural neutral order:

• verb + object + place

So:

• stendo = verb
• il copriletto nuovo = direct object
• sul letto = location

Italian word order is somewhat flexible, but this version sounds smooth and standard.

For example, Sul letto stendo il copriletto nuovo is possible too, but it gives more focus to sul letto. The original sentence is the neutral everyday choice.