I have a Dell Inspiron 7520 and had similar problems; basically the executable for the upgrade downloaded from the Dell site has to be run in a Windows 7 environment. If your machine is dual-boot with a Windows 7 option that is no problem, but if like me you have removed Windows entirely there are still ways to do the upgrade.
Check out my answer to this question. The key is to boot you computer into a Windows 7 command line mode, which can be done using a Windows 7 Repair Disk (not installation media!). If you have the executable on a USB drive it is then trivial to run it.
It is possible to make a small USB drive into a bootable Windows 7 Repair drive if you do not have a CD drive.
I obtained my Windows 7 Repair Disk by installing a copy of Win7 on a VirtualBox VM, but you can download them from the web, or find a friend with a Win7 machine to make one for you.