I've been trying to do this for 6 hours but my efforts were of no avail. I tried make changes to the pc and winalt folders in
/usr/share/X11/xkb/symbols/ but couldn't figure out the correct changes.
You should change something in
/usr/share/X11/xkb/keycodes/ instead. Find the file of your keyboard layout (mine is
evdev) and then modify the file. The file contains the name of the keys and numbers that correspond to the key. You should only switch the numbers of the LCTL key and the LALT key. Don't forget to delete all .xkm files in the
/var/lib/xkb/ directory and restart xorg. Proceed with caution, backup the file before you modified it.