How do I delete text messages from iCloud to free up storage?

In Messages and I am presuming that you are using Messages on the Mac, right click on the Message(s) you want to delete and click delete. While you are still in Messages, click on View and click on Recently Deleted The ones you just deleted will show up here. Highlight all the ones you don't want in the left hand bar and on the main page you should see a delete button.

You can't delete messages directly from iCloud. You can only delete the message from Message on a device connected to the iCloud account. That will delete them from iCloud.