Hi,

Please check the free space for system ts.

SQL> SELECT TABLESPACE_NAME, SUM(BYTES) FROM DAB_FREE_SPACE
GROUP BY TABLESPACE_NAME;

and try to find out how much of contiguous free space is available.
use that size to minimize your TS size by finding related datafile

EX :
SQL> alter database datafile '/disk1/oradata/XXXXX/system01.dbf' resize 2gb;


Regards,
Singh.