As suggested by AakashJ the best option would be to export the VM as OVF and copy the data to External USB drive and import them on the new site.
But would like to know why you want to move from ESX to ESXi? As from ESXi is only platform available from 5.x
And which version of ESXi are you running and what is the version of ESX? Make sure both version are same as you will have Virtual Hardware compatibility error if you move from higher to lower version