I have a customer who has a current vSphere 4 cluster and have bought an additional license but it's vSphere 5.
Can I use this license for vSphere 4? If so how do I use it?
you can't use a vSphere5 license for vSphere4. With that said, you can have the customer go to their license portal and "downgrade" the vSphere5 license. This will generate a new key for vSphere4. When you are ready to go to vSphere5, you can then "upgrade" License
you can't use a vSphere5 license for vSphere4. With that said, you can have the customer go to their license portal and "downgrade" the vSphere5 license. This will generate a new key for vSphere4. When you are ready to go to vSphere5, you can then "upgrade" License