Use a text editor to edit the keyboard layout configuration file:
sudo nano /usr/share/X11/xkb/symbols/us
change:
key <AE01> { [ 1, exclam ] };
key <AE02> { [ 2, at ] };
key <AE03> { [ 3, numbersign ] };
key <AE04> { [ 4, dollar ] };
key <AE05> { [ 5, percent ] };
key <AE06> { [ 6, asciicircum ] };
key <AE07> { [ 7, ampersand ] };
key <AE08> { [ 8, asterisk ] };
key <AE09> { [ 9, parenleft ] };
key <AE10> { [ 0, parenright ] };
to:
key <AE01> { [ exclam ] };
key <AE02> { [ at ] };
key <AE03> { [ numbersign ] };
key <AE04> { [ dollar ] };
key <AE05> { [ percent ] };
key <AE06> { [ asciicircum ] };
key <AE07> { [ ampersand ] };
key <AE08> { [ asterisk ] };
key <AE09> { [ parenleft ] };
key <AE10> { [ parenright ] };
Save the file and apply changes using this command:
setxkbmap us
You might need to restart.