You can extend a vRAM pool of a certain license edition in three ways.
1.Assign new license keys of the same edition to unlicensed ESXi 5.0 hosts.
For example, the total amount of memory that you provision on the powered-on virtual machines on ESXi 5.0 hosts that are licensed with vSphere Standard reaches the maximum amount of pooled vRAM for vSphere Standard. To increase the vRAM pool for vSphere Standard, you assign another license key of vSphere Standard to an unlicensed ESXi 5.0 host.
2.Combine a license key of the same edition
You can combine the capacities only of license keys that are of the same vSphere 5.0 edition.
For example, suppose that you license a group of ESXi 5.0 hosts with license key A of vSphere Standard. License key A has a capacity of 10 processors and adds 320GB of vRAM to the pool for vSphere Standard. The amount of consumed vRAM for vSphere standard reaches 320GB. You purchase license key B of vSphere Standard that has a capacity of 5 processors corresponding to a vRAM entitlement of 160GB. You use the VMware Licensing Portal to combine the capacities of license key A and B to create license key C of vSphere Standard that has a capacity of 15 processors. You remove license key A from the ESXi 5.0 hosts and assign them the new license key C. Respectively, the vRAM pool for vSphere Standard is extended to 480GB.
3.Upgrade the editions of the license keys that are assigned to ESXi 5.0 hosts.
For example, you can upgrade the license keys from vSphere Standard to vSphere Enterprise. License keys of vSphere Enterprise entitle 64GB of vRAM for the processor capacity of the license key.
If you license vCenter Server with a vCenter Server Essentials license key, you must consider the following limitations.
You cannot power on a virtual machine through a direct connection to an ESXi host.
You cannot hot add memory to a virtual machine through a direct connection to its ESXi host.
For powered-on virtual machines on the hosts that vCenter Server manages, you cannot configure more memory than the vRAM that is provided by the host license keys.