How to safely remove parameter

Hello,

DB16 is warning me that my Oracle DB (version 10.2.0.4.0) has the following parameter set:

OPTIMIZER_FEATURES_ENABLE

Which, according to SAP note 830576 ("Parameter recommendations for Oracle 10g), shouldn't be set.

However, it has the value "10.2.0.1".

I've searched and found this thread, here at SCN:

Changing or Deleting Oracle DB Parameter Using BRTOOLS

This thread has the following instructions:

SQL> create pfile from spfile;

Edit the pfile according to your needs

and after this:

sql> shutdown immediate

sql> create spfile from pfile;

sql> startup

Also, there will be many parameter which will take default value if you do not set it.

Since I'm an Oracle newbie, I'm wondering:

1st) Where will the pfile be created?

2nd) How can I be sure that I don't have any problems related to the last sentence: "Also, there will be many parameter which will take default value if you do not set it."

thanks

Antonio