When done changing settings press Ctrl + S to save the cfg file. Note: Make a backup copy of any cfg file your about to change that includes this one. I entered 16 as that number seems to be the best on most maps, I wouldn't go any higher unless you have a decent processor.
Now that the gamemode_casual.cfg is open look for bot_quota witch should be almost at the beginning of file, and change the number to what ever you want.
Navigate to C:\Program Files (x86)\Steam\SteamApps\common\Counter-Strike Global Offensive\csgo\cfg and drag the gamemode_casual.cfg file into notepad.
To do that press Windows + R to open Run and type notepad followed by ok To change the number of bots we first need to open the gamemode_casual.cfg file.