Normally not needed. Unless you've 'hacked' your installation, RMS automatically updates itself each morning when it starts up. If for some reason you've disabled this, then you will need to manually run the script in a terminal window:

Scripts/RMS_Update.sh

After running an update you should reboot the Pi.

sudo reboot

Yes. Unlike windows, the Pi does not force patches and updates on you. However you should definitely periodically check and apply any patches. To do this open a terminal window and type:

sudo apt-get update && sudo apt-get upgrade

You'll get a list of updates, press Y to continue. We recommend doing this monthly, otherwise the list of updates can become huge, and you may experience stability problems. After running an update you should reboot the Pi.

sudo reboot