I’m new to Linux. 
How do you update it? I guess if you just download the new update on your computer, drag it into your SD card, it will delete every app that you downloaded and files that you made.
I am not certain if it is identical for the pi as for x86. but the normal procedure is simply:
sudo apt-get update
sudo apt-get upgrade
None of the above will delete any apps you have individually downloaded or any personal files you have created
There’s also this one:
sudo apt-get dist-upgrade
And for updating the Raspberry Pi kernel:
sudo rpi-updateSee also (generally for PC’s but I think you can do almost all of what is written on Raspi?):