If you decide to upgrade your game server from standard range to premium range, the process would be via the normal upgrade process Here except that the service switch require manual process from our side since we need to move your service from one server range to another. In light of this, please submit a ticket with your order number to our support and we will switch you to your new range within minutes.
Side Note:
The switch will wipe your server data, files, mods, plugins, saved content .. etc so make sure that you have a backup in your local PC in order to upload them again to your new range OR ask the support to do that process for you in order to save time as we provide full support of moving service from one range to another.