You will need some hardware and specialized software to do that...
I'll refer you to these references, youtube.com/watch?v=WppfGkNm-WU & signvideo.com/conv-v-to-d.htm
If you can't do that yourself due to the hardware required and you only have to do it once or 3 times... I think it's more practical to let someone do it. I'm sure there are services in your area that offers such type of service.
However, if you do this for lots of VHS tapes, we're talking of more than 10 or even 100s, then...I think it's worth getting such accessories and peripherals and do it yourself.