How to change the "Alternative switch to next source"

Finally I found the option. I had to install Tweaks and go to

Keyboard and mouse > Additional layout options > switching to another layout

The strange thing is that there is that the default shortcut super+space was not selected in that window, only the alternative shortcut.

In my answer I assume that you use Gnome 3.x.

You can use Tweaks, but you can also write the value directly, for example, changing from Alt+Shift to Ctrl+Shift can be done by the following command in terminal:

dconf write /org/gnome/desktop/input-sources/xkb-options ['grp:ctrl_shift_toggle','grp_led:scroll']

To disable the option of alternative switch to the next source type in terminal:

xkbopts="/org/gnome/desktop/input-sources/xkb-options"
dconf read $xkbopts
dconf write $xkbopts "['']"

This worked for me. No reboot is necessary.