Checklist Before Upgrading to Windows 10
Ensure you have created Windows 7/8.1 USB Recovery Media using Dell Backup and Recovery version 1.8.7.2 this will allow you to reinstall your old Windows version should something go wrong with the upgrade:
http://dellwindowsreinstallationguide.com/dell-backup-and-recovery-1-8-1-71/
Update your BIOS to the latest version. Windows 10 may fail to install in many systems without the latest BIOS:
http://dellwindowsreinstallationguide.com/updating-the-bios/
Downloading and Creating Windows 10 Installation Media
To Download Windows 10 and Create a Bootable USB setup for a UEFI BIOS with SecureBoot (recommended if your system is >2011) or a Legacy BIOS (if your system is <2011) see:
http://dellwindowsreinstallationguide.com/download-windows-10-oem-and-retail-iso/
Wiping a SSD/HDD
Requires Windows 10 Installation Media. To wipe your SSD/HDD see here:
http://dellwindowsreinstallationguide.com/cleaning-up-a-drive-format-vs-secure-wipe-ssd-and-hdd/
Clean Installation
Windows 10 TH2 can be directly clean installed using your Windows 7 OEM or Windows 8.1 OEM key. See here for details:
http://dellwindowsreinstallationguide.com/download-windows-10-oem-and-retail-iso/#CleanReinstallation
More details here:
http://dellwindowsreinstallationguide.com/a-clean-install-of-windows-10/
Notes on System Drivers
Checking your hardware IDs to identify system variants in the device manager:
http://dellwindowsreinstallationguide.com/checking-hardware-ids-in-the-device-manager/
Make a new post on the forum providing your Version and architecture of Windows, model number and hardware IDs:
http://en.community.dell.com/support-forums/software-os/f/4997
Notes on Dell Driver Installation Order:
http://dellwindowsreinstallationguide.com/2015/09/27/driver-installation-order-windows-10/