How do you change the storage parameters of a already made table (sql developer)?
The extent parameters can not be changed of an existing table, they are specified when a table is created. You can change them by reorganizing the table.
SQL&gt; select INITIAL_EXTENT, NEXT_EXTENT, MAX_EXTENTS, PCT_INCREASE
     from user_tables where table_name = 'T1';

INITIAL_EXTENT NEXT_EXTENT MAX_EXTENTS PCT_INCREASE
-------------- ----------- ----------- ------------
         65536     1048576  2147483645

SQL&gt;  alter table t1 storage(initial 1048576 next 2097152 maxextents 1073741822 pctincrease 1);
 alter table t1 storage(initial 1048576 next 2097152 maxextents 1073741822 pctincrease 1)
                        *
ERROR at line 1:
ORA-02203: INITIAL storage options not allowed


SQL&gt; alter table t1 storage(next 2097152 maxextents 1073741822 pctincrease 1);
alter table t1 storage(next 2097152 maxextents 1073741822 pctincrease 1)
*
ERROR at line 1:
ORA-25150: ALTERING of extent parameters not permitted


SQL&gt; create table t2 storage (initial 1048576 next 2097152 maxextents 1073741822 pctincrease 1)
     as select * from t1;

Table created.

SQL&gt; select INITIAL_EXTENT, NEXT_EXTENT, MAX_EXTENTS, PCT_INCREASE
     from user_tables where table_name in ('T1', 'T2');

INITIAL_EXTENT NEXT_EXTENT MAX_EXTENTS PCT_INCREASE
-------------- ----------- ----------- ------------
         65536     1048576  2147483645
       1048576     2097152  2147483645

Notice how the MAX_EXTENTS and PCT_INCREASE parameter did not change. They are relevant only for dictionary managed tablespaces, but that was forgotten ages ago, we use locally managed tablespaces.