Upgrading from VMware vCenter Essential 5.0 to VMWare vCenter Essential plus 5.0

Hi All,

I have a client who actually have 2 servers with ESXI 5.0.  They are currently managed by vCenter 5.0 and licensed with VMware vSphere Essential.  Now the client want to do HA and vMotion and thus has requested to upgrade the license of existing host to vSphere Essential Plus 5.0.

Now I want to know:

1. How this is done,is it just a matter of clicking on licensing tap and changing the product key to the new vSphere Essential plus?

2.  The client currently have Storage API, add-on, etc, will the upgrade affect these APIs and ADD-On?

Thanks

Nicolas