I have a lot of space on my iCloud, how i can transfer my documents from storage to icloud

iCloud is a syncing system, not an external 'hard drive'. If you delete them on your device, they will delete from iCloud. To increase space available, go Settings/Your Name/iCloud/Photos and select Optimize iPhone/iPad Storage. That will reduce the space required by about 90% when fully effective.

For what you want to do, you need a different cloud based solution such as Dropbox, OneDrive, or Flicker.