I use Canopus Procoder 2 for most of my editing needs, but first you will have to get the VOB's onto your hard drive (either extract from ISO or rip) Isobuster and DvDecryptor will do this.
Once on the HD I tend to work on one VOB at a time as Canopus is very CPU intensive.
As to a tut I would pay a visit to
www.videohelp or doom9's sites, not that Canopus is incredibly complicated tho you could probably work through the menus and make it do what you want.
Here is a quick "snapshot" guide to resizing using Canopus:
1: Source Tab Add "source" in this case VOB file/s.
2: Target Tab Add/DVD then select the format you need (try to keep it the same as the original it transcodes faster).
3: Still in Target window select: Advanced/Video Filter/Add then select Crop click for cropping rectangle and resize as you like.
4: Convert Tab Convert and your done!
Canopus is a very powerful tool and will do lots of other clever things, the above is only for resizing.
@Sameira yes the quality will degrade as you are effectively zooming in but I guess how much depends on the quality of the original files you are working on.