TL;DR;
Your sentence "Ich ziehe meine Kleidungen um" is wrong. You either put clothes on or off, but umziehen can only be used reflexive without any object. "Ich ziehe mich um". Period.
Further elaboration
Ich ziehe mich um.
means that you change your clothes. You don't need to be more specific, this sentence is very clear.
Similar,
Ich zieh mich an.
Ich zieh mich aus.
means to get dressed or undressed.
There's really no need to add the word clothes.
If you really want to phrase a sentence using clothes, you can use the literal translation for "I change my clothes", which is:
Ich wechsel meine Klamotten.
Not that common, though.
That being said, context is certainly important and the context is what makes clear what exactly you're changing. Clothes yes, for sure, but which clothes? Your entire outfit? Just the shirt? This information is usually given with the context:
- Ich ziehe mich um und gehe schlafen. -> You put on your pajamas.
- Ich ziehe mich um und dann können wir losgehen. -> You put on your party outfit.
- Mir ist warm, ich ziehe mich um. -> You put on some clothes that are less warm.
That's again true for aus- and anziehen:
- Ich ziehe mich an, dann können wir losgehen. -> You're currently wearing your pajamas, just underwear or you're even naked, and you'll put on your clothes to go out.
- Ich ziehe mich aus und gehe ins Bett. -> You're getting undressed. You're getting ready for bed. Maybe you put on some pajamas, but that's not for sure.
If you want to tell what exactly you change, there are many possibilities. However, you can't use sich umziehen. Instead you take ausziehen and anziehen, which can be both reflexive and non-reflexive. That means, you can add (and this is pretty common indeed) the reflexive mir. But you can go without it or you can even apply any other dative object.
- Ich ziehe meinem Kind einen wärmeren Pullover an.
- Ich ziehe (mir) meinen Schlafanzug an.
- Ich ziehe (mir) die Socken aus.
- Ich ziehe meine Freundin aus.