Hello Mart,
updates for Linux Lite OS and tools are not available through Ubuntu repositories, these are for Ubuntu updates, including the upstream base of Linux Lite.
Updates for Linux Lite and Ubuntu upstream base, plus any additional softwares you have installed are all done by using -
Menu>favorites>Install Updates
Which will connect to LL repos, Ubuntu repos, PPA and other installs you have made, to gather the updates.
Lite Sources is to choose which server location/mirror you wish to download your updates from.
If Lite Sources is not used to select a server, I am not sure if it will just use a default server as I use an older version of Linux Lite without Lite Sources.
updates for Linux Lite OS and tools are not available through Ubuntu repositories, these are for Ubuntu updates, including the upstream base of Linux Lite.
Updates for Linux Lite and Ubuntu upstream base, plus any additional softwares you have installed are all done by using -
Menu>favorites>Install Updates
Which will connect to LL repos, Ubuntu repos, PPA and other installs you have made, to gather the updates.
Lite Sources is to choose which server location/mirror you wish to download your updates from.
If Lite Sources is not used to select a server, I am not sure if it will just use a default server as I use an older version of Linux Lite without Lite Sources.