You Can Find BIOS Version 1.70 on Dell's Driver Website Here
The bad news is that it is a Windows process, meaning you have to do it in Windows. The good news is that it a completely automated process and impossible to mess up. All you have to remember is that you need to have your Inspiron plugged in when you update the BIOS. If your not plugged in, you'll brick your laptop.
There are other ways to update your BIOS, but I don't feel comfortable writing a guide or recommending them to my readers. So many things can go wrong, especially when updating via the DOS command line.
edited by pHreaksYcle