heya no moyougae wo suru.

Here, の links two nouns:

• 部屋 = room
• 模様替え = rearrangement / redecoration

So 部屋の模様替え literally means the room's rearrangement, but in natural English it is more like rearranging the room or redecorating the room.

This の is not only for possession. It often means related to, for, or about.

模様替え usually means changing the look or arrangement of a space.

For a room, that often includes things like:

• moving furniture around
• changing the layout
• changing curtains or decorations
• giving the room a new feel

It does not usually imply major construction. It is more like rearranging or redecorating than renovating.

Because 模様替え is functioning as a noun, and する means to do.

So the pattern is:

• Noun + をする

That is a very common structure in Japanese, for example:

• 勉強をする = do studying / study
• 掃除をする = do cleaning / clean
• 模様替えをする = do a rearrangement / rearrange

In this sentence, the thing being done is 部屋の模様替え.

Yes, often you can.

Both of these are possible:

• 部屋の模様替えをする
• 部屋の模様替えする

The version with を sounds a little more explicit and structurally clear. The version without を is common too, especially in casual speech.

For learners, 部屋の模様替えをする is a very safe pattern to use.

The sentence you were given treats 部屋の模様替え as one noun phrase: the room's rearrangement.

So the structure is:

• [部屋の模様替え] を する
• do [the room rearrangement]

You may also hear 部屋を模様替えする, where 部屋 is treated more directly as the thing being rearranged/redecorated.

Both can be used, but 部屋の模様替えをする is a very common and natural way to say it.

Japanese often leaves out the subject when it is clear from context.

So this sentence could mean things like:

• I rearrange the room
• I will rearrange the room
• We are going to rearrange the room
• simply to rearrange the room as a dictionary-style example

The subject is omitted because Japanese does that very often.

する is the plain form.

You often see the plain form in:

• dictionary entries
• example sentences
• casual speech
• to-do lists
• written descriptions of actions

The polite version would be:

• 部屋の模様替えをします。

So the sentence is not less correct; it is just less polite and more neutral/basic in form.

Japanese non-past forms can cover both.

So 部屋の模様替えをする can mean:

• do / am doing in some contexts
• will do in other contexts
• or just the general action to rearrange the room

Context tells you which reading is intended.

It is read:

• もようがえ

A learner might expect かえ from 替え, but in this compound it becomes がえ. This is a common sound change in Japanese called rendaku.

So:

• 部屋 = へや
• 模様替え = もようがえ

Full reading:

• へや の もようがえ を する

No.

• 掃除する = to clean
• 片付ける = to tidy up / put things in order
• 模様替えをする = to change the arrangement or decor

You might clean or tidy while doing a 模様替え, but the main idea is changing how the room is set up or looks, not just making it neat.

Usually no.

模様替え suggests a lighter change, such as:

• moving furniture
• changing decorations
• changing the room's layout or appearance

For bigger changes, Japanese more often uses words like:

• 改装する = remodel / renovate
• リフォームする = renovate, refurbish
• 改築する = rebuild / structurally alter

So 模様替え is more like a makeover, rearrangement, or redecoration than a major renovation.