Well, This can get a little tricky depending on your setup, but here's
a few things you should know before you start.
Boot order is determined by your BIOS, which is inaccessible to the
blind. Dell offers a quick boot option by tapping the F12 key on boot
up, which will offer a few boot devices in a list, such as CD/DVD,
USB, Network, ect...
However, this probably won't work for you and here's why. The USB
option offered in the quick boot menu is run in legacy mode and you
can't install the new OS in that mode.
You'll need to get into the BIOS and make the USB drive the first
bootable option, Enable Uefi mode and disable the secure boot option.
Further, you need to format the USB drive using the FAT32 file system
and have the 64bit version of Windows 10 on it ready to go.
Sorry I don't have any work a rounds for this one,