Dear Seng,
There are a couple of paths here, and I'm not 100% sure which one you are looking to follow.
Path 1. Upgrade environment from 4.7 to K2 Five, with no workflow rebuild.
As previously mentioned, as long as the workflows were not built in k2.net 2003, your 4.7 workflows will continue to run in Five. No rebuild required. This is true for all currently available "versions" of K2 Five (up to and including 5.3).
Path 2. Upgrade 4.7 or build new K2 Five environment, "convert" or rebuild workflows using new K2 Five/HTML Designer.
Again, your 4.7 workflows will continue to function. When you rebuild, you will create new workflows in the HTML Designer, which will be distinct from the old workflows. Instances started on the old workflows will need to complete against the old workflow version.
You can either build your workflows from scratch, or you can use third-party tools (such as Jeylabs PowerToolz Express) to analyze and help convert your workflows.
I hope this helps,
Gail