Extract the DVD ISO using Imgburn or download another, write to flash stick using Universal USB Installer
with Win7 in dropdown menu. Boot under USB, REmovable or HD's using one-time BIOS Boot Menu key with HD set to boot first in BIOS setup.
The disk are all the same: upgrade, full, retail, OEM. It is the key which determines which version will activate.
Other tips including the latest ISO are here: Clean Reinstall - Factory OEM Windows 7,
same for retail.