I am going from memory at this point but in general take your DVD (preferably as decrypted/sanitised files or with something like anydvd but it does have basic css, region unlocking and PUOP removal if you are dealing with an older dvd/one without corrupted sectors) and on the right hand pane there tab there should be an option to build your own DVD. From this find the main video (usually the longest video but be aware some extras can run longer than the film so check it with the preview option) and drag it to the new DVD structure (should be on the left hand pane) and the rest amounts to pressing go, choosing a location and watching it do it.
If on the other hand you want to retain menus it can more tricky. I am not sure of the suggested method these days but assuming I was being lazy I would normally use vobblanker. It is not quite as effective (the blanked videos can still be several hundred megabytes depending on length) but it works and is far nicer than having to play with something like PCGedit (and learning PCGedit in the first place) for hours on end.
I will however note that last I checked the free version of DVDfab had the ability to do this right from the DVD.