How to enable Automatic Memory Management (AMM) in 11g

check the existing value

SQL> SHOW PARAMETER target

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
archive_lag_target                   integer     0
db_flashback_retention_target        integer     1440
fast_start_io_target                 integer     0
fast_start_mttr_target               integer     300
memory_max_target                    big integer 0
memory_target                        big integer 0
parallel_servers_target              integer     128
pga_aggregate_target                 big integer 6700M
sga_target                           big integer 10048M

Run the following statement

 SQL> ALTER SYSTEM SET memory_max_target=15G SCOPE=SPFILE;
 SQL> ALTER SYSTEM SET memory_target=15G SCOPE=SPFILE;
 SQL> ALTER SYSTEM SET sga_target=0 SCOPE=SPFILE;
 SQL> ALTER SYSTEM SET pga_aggregate_target=0 SCOPE=SPFILE;

Shutdown and startup

SQL> shutdown immediate;
SQL> startup