You can transfer the ownership of a file to another user. When a file is transferred, it will use the Drive storage space of the new user instead.
1. Open the sharing settings of the document you wish to transfer by clicking Share in the up right corner.
2. Share the document to the user you wish to transfer the file to.
3. Re-open the sharing settings.
4. Change the sharing rights of the new owner-to-be to Is owner.
5. Save changes.