The quickest way is probably going to be to upgrade your 5.0 host to 5.5. At that point, it can be managed by a vCenter 6.5, then you can migrate your VM over to a 6.5 host.
If you cannot upgrade the current host, or run an earlier version on the new host (and vCenter), then it may be an option to test your backup, i.e. to restore the VMs from it on the new environment. Another option is https://www.virtuallyghetto.com/2012/06/how-to-copy-vms-directly-between-esxi.html.
You could export the desired VMs into .ovf format, and import then back in your new enviroment.
Another option is to download the VM folder (including .vmdk, .vmx, etc) to a local disk, upload it to a datastore in your new environment, and register it browsing the .vmx.
Remove the VM from old VCenter using remove from inventory option and register on new vcenter