There's not really a best method when it comes to licensing. What you may want to check first is that you are eligible for a license upgrade (requires your SnS be current), and this way you'll know if there are account issues that need to be resolved prior to you beginning the upgrade. After hosts are upgraded, they will operate in evaluation mode for 60 days until licensed.
Hello Uday ,
I would suggest you to operate the ESXi hosts in evaluation mode for 60 days as evaluation mode would have enterprise plus licence .
You could then contact the VMware licencing team to request for the new licence.
Yes, we are eligible for a license upgrade...and thanks for your reply we will proceed the same way.