I am planning to switch my desktop environment and I am a noob with linux and ubuntu and I just use it as it is no other software is installed but now I want to change to a different desktop enviroment and my question is that will I still get updates or will it be rooting an android phone I will not get any updates. Also will I be able to keep the applications like Firefox and libre office to my new desktop (lxde).
Changing your desktop system does not prevent your computer from getting updates.
You may no longer see notifications about updates, as they are targeted at displaying on the default desktop system. You also may find it harder to run graphical programs to perform updates, as they are built for Gnome.
You can always use the command line to do updates: