Before you resize an existing datafile, you should determine how much space is available on the disk.
Use the monitor_resize utility to resize an existing datafile. Resizing an existing datafile, instead of adding a new one, does the following:
Keeps the number of Oracle datafiles to a minimum when allocating more space for data
Simplifies the administration of datafiles.
 | Note: Do not make a datafile larger than 2 GB. |
To resize an existing datafile
Run the monitor_resize utility by typing
monitor_resize (Solaris) or bash monitor_resize (Windows)
When prompted, type the name of the tablespace.
Type the file name for the datafile you want to resize;
For example:
/usr/mvf/data/dbase/data1/mvf03.dbf (Solaris)
E:\data\dbase\data1\mvf03.dbf (Windows)
Type the new size of the database in megabytes (such as 2000).
The following message appears:
Monitor statistics are updated.