Oracle Database Discussions

Hi, I am trying to activate auditing in an Oracle 9i database but it seems a bit complicated.
Right now Auditing is disabled (audit_trail = none)
If I am not wrong I must set this:

AUDIT_TRAIL = TRUE
(I want to collect the data in SYS.AUD$ table)

It seems that to enable this option I have to reset Oracle.
The question is, where do I exactly write this parameter?

Do I edit the spfile.ora with a text editor, I heard it is not a good idea?

SQL: show parameter pfile;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
spfile string ?/dbs/spfile@.ora


thanks