(or whereever you have installed your FirstStrike directory, but it is the ai folder you need).

Locate the file titled aidefault and open it with word. It does have instructions, but just remove these lines:

aiSettings.overrideMenuSettings 1
aiSettings.maxBotsIncludeHumans 1
aiSettings.setMaxNBots 24
aiSettings.setBotSkill 0.5
sv.ticketratio 100

and replace them with these lines:

aiSettings.maxBotsIncludeHumans 1
aiSettings.setMaxNBots 16
aiSettings.setBotSkill 0.4

Changing the MaxNBots will change how many bots you have, and by removing the line OverrideMenuSettings, you can now change bot difficulty.

WARNING

This will prevent you from being able to play FS on a server since you will now have a modified file. If you wish to play online then first copy the original file to a different location so that you can quickly restore it if required.