How to extend rollback segment ?

ALTER ROLLBACK SEGMENT RBS_04 STORAGE (OPTIMAL 500M);

query was success.

but when I try to find a total rollback tablespace size it is showing old value ?

was it extended or not ?
and

how to find allocated space for all rollback segments ?

After that i try to fire a below query--

prd176> ALTER ROLLBACK SEGMENT RBS_04 STORAGE (MAXEXTENTS 65530);
ALTER ROLLBACK SEGMENT RBS_04 STORAGE (MAXEXTENTS 65530)
*
ERROR at line 1:
ORA-02221: invalid MAXEXTENTS storage option value

how to check valid maxextents ?

finally :

customer got ORA-01555 error, and database having rollback segments ( not undo tablespace ) , becuase of rollback segment RBS_04 , customer got that error, so how to extend the segment RBS_o4., first I need to find the allocated space for RBS_04 but how ?

prd176> SELECT SEGMENT_NAME,TABLESPACE_NAME,FILE_ID,MAX_EXTENTS,MIN_EXTENTS
FROM DBA_ROLLBACK_SEGS
2 3 ;
Tablespace
SEGMENT_NAME Name FILE_ID MAX_EXTENTS MIN_EXTENTS
-------------------- -------------------- ---------- ----------- -----------
SYSTEM SYSTEM 1 505 2
RBS_01 ROLL_T01 2 32765 1
RBS_02 ROLL_T01 2 32765 1
RBS_03 ROLL_T01 2 32765 1
RBS_04 ROLL_T01 2 32765 1
prd176> @tbspace_info
Tablespace Size Used Free Pct. File TS Ext
Name (MB) (MB) (MB) Used Count Type Mgmt
------------------------------ -------- -------- ------- ------- ----- ---- -----
USERS_T01 41 0 41 0.30 1 PERM LCL-A
TOOLS_T01 76 0 76 0.16 1 PERM LCL-A
SYSAUX 501 352 149 70.22 1 PERM LCL-A
TEMP_T01 500 299 201 59.72 1 TEMP DICT
GLOBAL2_DATA_T01 1001 679 322 67.79 1 PERM LCL-A
SYSTEM 600 275 325 45.90 1 PERM DICT
GLOBAL2_INDEX_T01 901 513 389 56.88 1 PERM LCL-A
ROLL_T01 1000 21 980 2.05 1 PERM LCL-U
EMADOCS_DATA_T01 9626 7041 2585 73.15 6 PERM LCL-A
DMS_AUDIT_DATA_T01 56508 51871 4637 91.79 15 PERM LCL-A