If you’ve deployed a vault with the Standard sku and would like to update it to Premium, it currently isn’t possible to do so using the portal. Although CI/CD tools support setting the sku at creation time, some of them don’t handle changing the sku. For example, Terraform plan will notify you that the sku is going to be updated, but it doesn’t actually happen when you apply the change. The next time you run Terraform, the sku hasn’t been updated and so Terraform once again says it’s going to change the sku. There is an easy solution: azure cli.
az keyvault update --set properties.sku.name=premium --name <vaultname> --resource-group <rgname>
That’s all there is to it. The json output will reveal the new Premium sku and, of course, you can confirm via the portal.