The following instructions will guide you through configuring Ubunutu 18.04 LTS on a Dell XPS 13 (9370) that came pre-installed with Windows 10;

It is highly recommended that you have various backups available before starting this i.e. full image backup, files backed up and a restore point is created before starting this.

Shrink Windows volume to create space for Ubuntu

Using Disk Management in Windows, shrink an existing volume by at least 25GB to create space for the Ubuntu OS

Turn off Bitlocker (If enabled)

  1. Click Start, Control Panel, System and Security, and BitLocker Drive Encryption.
  2. Look for the OS drive on which you want BitLocker Drive Encryption turned off, and click Turn Off BitLocker.

Turn off Fastboot

Right click Start and select Power Options, select Additional Power Settings on the right hand side
Select choose what the power buttons do
Select change settings that are currently unavailable
Uncheck "Turn on fast startup (Recommended)"

Disable secure boot and enable USB boot support

Restart your machine and hit F12 on the dell logo screen to pull up the boot options
Select BIOS Setup

Under Secure Boot > Secure Boot Enable, ensure secure boot is set to disabled

Under System Configuration > USB Configuration, ensure Enable USB Boot Support and enable external USB port is selected

Under POST Behaviour > Fastboot, ensure this is set to Thorough

Apply and Exit, reboot into windows to ensure everything is working correctly with the changes made

Change from RAID to AHCI 

This step is only required if your SATA configuration is set as RAID, attempting to change it without the correct controller installed will cause boot issues, to add the controller complete the following steps;

Right click command prompt and Run as Administrator
Type the following to force a safe mode boot bcdedit /set {current} safeboot minimal
Restart your machine and hit F12 on the dell logo screen to pull up the boot options
Select BIOS Setup
Expand System Configuration and select SATA operation
Switch from RAID to AHCI and click Apply
Save and exit to boot into Windows 10 Safe mode
Right click command prompt and Run as Administrator
Type bcdedit /deletevalue {current} safeboot to disable safe mode boot
Restart your laptop, ensuring laptop boots succesfully into windows
Within Device Manager, there should now be a Standard NVM Express Controller device under Storage Controllers

Prepare Ubuntu

Using a 4GB USB memory stick, Rufus and the latest Ubuntu LTS
Prepare a bootable USB stick then attach USB and reboot laptop

You should now see the USB and you may need to check your boot order by pressing F2 when attempting to boot from USB.

Follow the Ubuntu wizard to install Ubuntu on the 25GB volume created earlier

You should now have option to load Ubuntu or Windows 10 everytime the laptop boots up.