how to delete message storage in icloud

Hello fatty29,

Thank you for posting to Apple Support Communities.

Deleting messages, conversations, attachments and files from Messages can help resolve this. To see which content is using the most amount of space in iCloud and how to delete this, follow the steps below:

When you use Messages in iCloud, all of your text messages and the attachments you send and receive use your iCloud storage. You can make more space available when you delete texts and attachments—like photos, videos, and files—that you don't need anymore. 

Delete a message or attachment on your iPhone or iPad

1. In a message conversation, touch and hold the message bubble or attachment that you want to delete.

2. Tap More.

3. Tap Delete , then tap Delete Message. If you want to delete all messages in the thread tap Delete All, in the upper-left corner. Then tap Delete Conversation.

Delete multiple attachments from a contact or conversation

1. In a message conversation, tap the contact's name at the top of the screen.

2. Tap Info .

3. In the Photos section, tap See All. 

4. Tap Select, tap the images you'd like to delete.

5. Tap Delete, then tap Delete Attachment to confirm. 

Delete an entire conversation 

1. Swipe left over the conversation that you want to delete.

2. Tap Delete.

3. Tap Delete again to confirm. 

Delete a message or attachment on your Mac

1. Open a message conversation.

2. Control-click the blank area of a message bubble that you want to delete.

3. Choose Delete.

4. Click Delete.

Delete multiple attachments from a contact or conversation

1. Open a message conversation.

2. Click the Info button .

3. Scroll to the Photos section.

4. Click on an attachment then hold the Command key to select multiple attachments. 

5. Control-click or right-click, then choose Delete.

6. Click Delete Attachment to confirm. 

Delete an entire conversation

1. Control-click a conversation.

2. Choose Delete Conversation.

3. Click Delete.

This information is provided in Manage your iCloud storage - Apple Support.

Take care.