RESIZE Clause
This clause is valid only for bigfile tablespaces. It lets you increase or decrease the size of the single datafile to an absolute size. Use K, M, G, or T to specify the size in kilobytes, megabytes, gigabytes, or terabytes, respectively.
To change the size of a newly added datafile or tempfile in smallfile tablespaces, use the ALTER DATABASE ... autoextend_clause (see database_file_clauses ).