Remap Keys in Linux

"First off, try looking in Preferences > Keyboard > Layouts > Layout Options under the Alt/Win key behavior if there is a suitable option there for you.

If that doesn't do it for you, these xmodmap commands would switch left Ctrl with left Alt (at least with my keyboard).

xmodmap -e 'keycode 37 = Alt_L ISO_Prev_Group ISO_Prev_Group NoSymbol ISO_Prev_Group'
xmodmap -e 'keycode 64 = Control_L'

To get your keycode, you can run the program xev in a terminal window and press first Ctrl and note the keycode, then Alt to get the keycode."

"Do the following steps:

Create a new file. Let's call it remap.txt.
Add the following text to the file:

!
! Swap Alt_L and Control_L
!
remove mod1 = Alt_L
remove Control = Control_L
keysym Control_L = Alt_L
keysym Alt_L = Control_L
add mod1 = Alt_L
add Control = Control_L

The above is like a script for xmodmap. It will change the current key bindings.
Run the following commands to run the script:

# xmodmap remap.txt

(optional) To load the same settings after reboot run:

# sudo dumpkeys > ~/.Xmodmap"