kouishitsu de seifuku ni kigaeru koto ni natte imasu.

It is stipulated that we change into our uniforms in the changing room.

Breakdown of kouishitsu de seifuku ni kigaeru koto ni natte imasu.

• で: location particle
• に: indirect object particle
• 着替きがえる: to change clothes
• 制服せいふく: a work uniform

Questions & Answers about kouishitsu de seifuku ni kigaeru koto ni natte imasu.

Is 着替る correct here, or should it be 着替える?

In standard modern Japanese, it should normally be 着替える. So the sentence would usually be written:

更衣室で制服に着替えることになっています。

着替える is the dictionary form of the verb meaning to change clothes or to change into something.

What does ことになっています mean in this sentence?

V-ることになっています means it has been decided that..., it is مقرر / arranged that..., or it is the rule that....

So here, it does not sound like a personal choice. It sounds like an established rule, procedure, or arrangement. In context, it means something like:

It is the rule that you change into your uniform in the changing room.

Why is 着替える in plain form, not 着替えます?

Because the verb comes before こと, and before こと you normally use the plain form.

So:

• 着替えること = changing into... / the act of changing into...
• not 着替えますこと

The sentence becomes polite at the end with なっています.

What is こと doing here?