Disclaimer: If you are not comfortable editing the underlying configuration of Microsoft Flight Simulator then do not attempt to edit your FSX.cfg file. Instead, simply use the provided "sliders" within Flight Simulator.
Flight Simulator X creates an Application Data folder for the username that you use your computer under. If you do not use a particular user name on your computer - your user name is most likely "Administrator".
For most users - Your FSX.cfg file will be located at the following location (assuming C: is your system drive):
C:\Documents and Settings\USERNAME\Application Data\Microsoft\FSX
Where USERNAME is the user name you typically log in as.
IF YOU CAN'T FIND YOUR FSX.cfg file:
TweakFS has made a handy freeware utility that makes it a breeze for most users to directly edit their FSX.cfg file.
|TweakFS - FSX Config File Editor|
It can be downloaded here: TweakFS FSX Config Editor (TweakFS.com)
Always make a quick backup copy of this file before editing it.
A backup copy of that file will come in very handy should you ever want to rollback your changes.
It is recommended that you make only one change at a time to the configuration of Flight Simulator X and then start the simulator and observe the affect of the change. That way if there is a problem loading the simulator software, or some other behavior that you are unhappy with, you can easily know the change to rollback.
1. Always make backups
2. Make one change at a time