Deleting messages on iPhone to free up storage on icloud

Hi milagros271,

The steps to accomplish what you describe are covered in Manage your iCloud storage:

"Delete texts and attachments in Messages

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 the Delete button, 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. In the Photos section, tap See All. 
3. Tap Select, tap the images you'd like to delete.
4. 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."

You may also have to complete additional steps to permanently delete these items from the article Delete messages and attachments on iPhone:

"Permanently remove recently deleted messages and attachments

Deleted messages and attachments remain in the Recently Deleted folder for 30 days, but you can permanently remove them before that.

1. Open the Messages app  on your iPhone.
2. In the Messages conversation list, do one of the following:

• Tap Edit in the top-left corner, then tap Show Recently Deleted.
• Tap Filters in the top-left corner, then tap Recently Deleted.

3. If you’re in a conversation, tap  to return to the conversation list.

4. Select the conversations whose messages you want to delete permanently, tap Delete, then follow the onscreen instructions."

Regards.