VMware 3.5 to 5.5

I've been reading where we can't upgrade 3.5 to 5.5, which is fine. What I have read is we need to use V2V to migrate 3.5 VMs to 5.5. Is there a location to read up on how to use V2V for this or how to do this?

Also, where on vCenter 2.5 if this helps in our direction.

Any assistance over and beyond reading would be greatly appreciated!! Links, PDFs anything.   

Regards