How to determine if it is necessary to increase the sga and the pga in Oracle database
Tuning usually starts with a reason.  Oracle has made great strides in reducing the need to tune for many use cases.  Most tuning I have done has been necessitated by poorly written application code or trying to mix an OLAP application and reporting on the same instance. Without knowing your operating system and specifications, how the database is used, size of the OS paging file, number of users only general advice can be given.  The documentation is excellent and worth your time.

If you don't have a specific issue then set the aggregate PGA target parameter to 0 and let Oracle do the work. The existing settings can be seen here

SELECT *
  FROM V$PGASTAT;


Official documentation is here.

The SGA can also be automatically managed by Oracle with these settings:


STATISTICS_LEVEL to TYPICAL or ALL
SGA_TARGET to a nonzero value 
SGA_MAX_SIZE to a value larger than SGA_TARGET but small enough that there is enough memory free on the server for the OS and other running processes.  


You can query the existing settings from the SQL command line with

SHOW SGA


A very rough rule of thumb is to allocate at least four to six GB for the OS on a dedicated server.

Official documentation is here