To upgrade to Windows 7 Home Premium while keeping all your existing 
files/applications in place you obviously need to have Vista Home Premium on your 
computer. You also need to have Windows Vista Service Pack 1 or higher installed. I 
didn't and I could not update to it at first. 
However, you need to completely uninstall any anti-virus applications in order for Service Pack 1 to install properly.

I burnt the iso included in this torrent to a dvd disc using the excellent and free iso 
burner:

http://www.ntfs.com/iso_burner_free.htm

Once you have burnt your dvd then just install the dvd (do not boot from it unless 
you want a clean install) and then just open the dvd and double click 'setup'. All you need to do then is follow the instructions.

At the end of the process you will be asked to install a serial number. Use one of the
 following:

TWF78-W7H8T-KXD8C-YDFCQ-HK4WG
RHVHB-VYF67-9FT4M-2WXR8-P3C6R
Q8JXJ-8HDJR-X4PXM-PW99R-KTJ3H
PPBK3-M92CH-MRR9X-34Y9P-7CH2F
MVW82-3R7QW-Y4QDM-99M3V-C4QW3
BFTWY-X2PJR-VJP8V-KGBPJ-FWBMP
8489X-THF3D-BDJQR-D27PH-PJ3HC
4CBPF-W7GXG-J4J8F-GHG79-Q9YT8
38CGD-Q6RHB-37BVW-Y3XK7-3CJVC

Enjoy!