SQL> alter system set sga_max_size=7000m scope=spfile;

System altered.

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     0
memory_max_target                    big integer 0
memory_target                        big integer 0
parallel_servers_target              integer     96
pga_aggregate_target                 big integer 4820M
sga_target                           big integer 1536M
SQL> alter  system  set  sga_target=5000m scope=spfile;

System altered.

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area 7349010432 bytes
Fixed Size                  2214336 bytes
Variable Size            3019900480 bytes
Database Buffers         4294967296 bytes
Redo Buffers               31928320 bytes
Database mounted.
Database opened.
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     0
memory_max_target                    big integer 0
memory_target                        big integer 0
parallel_servers_target              integer     96
pga_aggregate_target                 big integer 4820M
sga_target                           big integer 5056M
SQL> show parameter sga

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
lock_sga                             boolean     FALSE
pre_page_sga                         boolean     FALSE
sga_max_size                         big integer 7040M
sga_target                           big integer 5056M
SQL> show sga

Total System Global Area 7349010432 bytes
Fixed Size                  2214336 bytes
Variable Size            3087009344 bytes
Database Buffers         4227858432 bytes
Redo Buffers               31928320 bytes