I want to disable archive log mode for my 11g database.

The steps I think should be followed are:

1. shutdown immediate;
2. Change the init.ora parameter related to the instance
In pfile:
log_archive_start = false
3. startup mount pfile='';
4. alter database noarchivelog;
5. alter database open;

What should the step 2 be, in case I have an SPFILE???? Please suggest.

Thanks in advance