Change the Oracle Parameters related to Archive log.

select * from v$parameter where name like '%arch%'

see the blow given parameters (and there are other parameters also) :

LOG_ARCHIVE_DEST

ALTER SYSTEM SET LOG_ARCHIVE_DEST='LOCATION=<path>/arch'

ALTER SYSTEM SET LOG_ARCHIVE_START = TRUE

Change the Database to archive log mode:

sqlplus / as sysdba

sql>shutdown immediate

sql>startup mount

sql>alter database archive log

sql>alter database open

 Now the database in Archive log mode.