need to change my I cloud storage plan

I need to reduce the storage plan from 2T 129.99 TL monthly to 200 GB with 39.99 TL.

When you want to downgrade your iCloud+ plan, see this Apple article: Downgrade or cancel your iCloud+ plan

Downgrade or cancel your iCloud+ plan - Apple Support (PH)

• Before you downgrade or cancel your iCloud+ plan, first download or remove content that exceeds your new storage amount. To make sure that you don't lose any information, learn how to copy what you store in iCloud.

👉 How to downgrade or cancel your iCloud+ plan on your iPhone, iPad, or iPod touch

1. Open the Settings app.
2. Tap your name.
3. Tap iCloud.
4. Tap Manage Account Storage or Manage Storage.
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6. 
   
7. Tap Change Storage Plan.
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9. 
   
10. Tap Downgrade Options and enter your Apple ID password.
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12. 
    
13. Choose a different plan:

• • To downgrade your plan, choose a new storage amount.
  • To cancel iCloud+, choose the free 5GB plan or choose None.

1. Tap Done. If you can't tap Done, make sure that you're signed in with the same Apple ID that you use for your iCloud+ plan. You can also try following these steps on a different device. If you still need help, contact Apple Support.

If you downgrade or cancel your iCloud+ plan, the change takes effect after your current subscription billing period ends.1

👉 1. Partial refunds are available where required by law. If you recently changed your iCloud+ plan, contact Apple within 14 days for a refund. Learn how to request a refund.

From: How to switch to a different subscription plan - Apple Support

On an iPad or iPhone:

1. Open the Settings app. 

2. Tap your name, then tap Subscriptions.

3. Tap the name of the subscription that you want to change.

4. Tap See All Plans, then follow the onscreen instructions to complete your purchase.

For other devices, read the support article.