Go into setup (F2 at powerup) and turn OFF IRST/RAID.  Save. Attach a Windows 10 install flash drive created with the Microsoft Media Creation tool  [URL]   Power up the system, pressing F2 a few times until a boot menu appears.  Boot from the flash drive and the Windows 10 installation will start.  You will need to repartition the disc for Windows 10 in GPT/EFI mode, but the installer will take care of that for you. If you want to leave the disc in IRST/RAID mode, you will need to have the Intel rapid storage driver on the flash drive, pause the install and load it before Windows can be installed to the drive.  
We had a professor load Ubuntu on their Dell laptop over Windows 10 OS we provided them with. Not dual boot but complete overriding and only Ubuntu on laptop now. Well after messing up the laptop, we here in IT are in the doghouse cause the laptop is not usable for the professor. Go figure. You would think it would be simple just boot to a Windows install USB and simple fix. No, not now with all these fancy EFI and BIOS on steroids PC now have.  I tried the posted suggestion of getting into the BIOS and deleting the Ubuntu boot partition from EFI. Windows could not see any drives. So, roadblock there. I then downloaded Ubuntu and placed on USB and booted to the USB drive.  Then went into Ubuntu’s disk manager and formatted the EFI and the data partitions on the drive from ext4 to NTFS.  Then tried Windows installer and Dell’s recovery tool. Both still do not see the drive. Roadblock two. Called Dell support and since this is not broken hardware can’t help. Yes laptop still under warranty but that seems only helpful if I ran over the laptop with my car. So how do I get Windows to see the drive that on the laptop so I can install Windows 10? I can’t find what hook Ubuntu still has that is hiding the drive from Windows. john
Latitude 3520, cannot remove Ubuntu to install Windows 10?