The Database can be changed to archive log mode as below.
Note: Archiving can be only applied in the mount mode.

Steps
1. Check whether the database is correct or not from v$database table.
     select name from v$database;

2. Check the log_mode from  v$database table.
    select log_mode from v$database;

3. Shut Down the data base and bring it to mount state.

4. Run the below command to set database in archive mode.
     alter database archivelog
5. Open the the database.


Checking database is in archive mode or not.
     
1. SQL> select name ,open_mode,log_mode from v$database;

NAME      OPEN_MODE  LOG_MODE
---------         ----------               ------------
DEVD     READ WRITE ARCHIVELOG

2. SQL> archive log list
Database log mode                Archive Mode
Automatic archival                   Enabled
Archive destination                  /archive01/DEVD/DEVD
Oldest online log sequence    11
Next log sequence to archive 15
Current log sequence              15