Hi folks the i3WM docs have good info on key mods
http://i3wm.org/docs/userguide.html#_default_keybindingsAlso if you want to edit the config file, its plain text in your home directory in the .config folder /home/yourname/.config/i3/config
As others have mentioned if you are really stuck you can go to another terminal (ctrl-alt-f2)and edit within your terminal text editor of choice (nano, vim, etc) - if your in the stock file manager with a gui (PCMANFM) then hit Ctrl-H to reveal the hidden folders to see the "dot files" navigate to the folder and edit in leafpad.....save then when done ctrl-H again to hide them if you dont want the clutter.
The top of that plain text config has an entry of set $mod Mod4 (which is the windows key)- change that to Mod1 and then save and restart i3, and you will have the alt key working as your modifier.
You can also change it to other keys, but thats beyond this post at this point.
As an aside, if you really want to play, you can delete (or I recommend rename) the config file, then restart i3, and "wizard" will come up to allow you to select your mod key, but you lose all the other customizations for apps, browser, etc. that are baked in wattOS.
Have fun....biff