Welcome to the Community - Are you using the vSphere client and connecting directly to the ESXi 5 host? If you are then you will not have an option to migrate as this is a feature of vCenetr.
Yo create an environment in vCenter the first step would be to create a Datacenter object - once that is done you would be able to right=click on the datacenter object in the inventory and one of the options would be to ad a host. Once the host is added to the vCenter environement you will have the migrate option on the VM drop down menu