While some updates on your device should happen automatically (like Windows Updates), some need to be manually run.
Thankfully your Dell XPS has an update utility that is easy to use.
Firstly, go to your start menu
and search for "Dell Update"
Your first hit should be the right one, as shown below
This will open the Dell Update utility which will search for and download all updates specific to your laptop model.
Most of the time, when these updates are completed, your laptop will need to be restarted to complete the installation.
NOTE: Some updates will only be available while connected to power, and will be greyed out if running on battery.
Often, these power dependent updates are BIOS updates, and wont actually install until you've restarted your laptop, in these cases it is very important to keep your laptop charging through the install process.
You'll know the BIOS update is being done if you see this screen after a restart:
If you get the following screen when checking for updates, you'll know you are up to date: