You should be able to connect a SATA SSD drive to the SAT0 port where the current HDD is connected. You don't have to install Win 8 first since Win 10 is already installed. The product key for Win 10 should be stored in BIOS so it should automatically get activated.
Create a bootable UBS stick with the Win 10 iso. Connect the USB and then power on. Immediately press F12 and select the option to boot from USB.
Unlikely you'll need to make any BIOS changes from current settings if Win 10 was already running from the HDD.
The white SATA connector ODD2 port may be reserved for an optical drive.
Forum Member since 2004
I am not a Dell employee