Alwyzon servers can be upgraded at any time over the client area. If you used one of the preinstalled operating systems, your disks will automatically resized too. Manual steps are only required if you installed the operating system yourself using your own ISOs.
To initiate an upgrade, login to the client area and select "More" > "Upgrade/Downgrade" in the upper right corner of the server management view. The form will ask you whether to upgrade your plan or to add/remove any addons. Please be aware that while you can remove addons at any time, it is not possible to downgrade plans once you upgraded yours.
There are no setup fees involved with upgrading, but you will be charged for the full billing period even if you are at the end of your present billing period. There is no pro-rata billing available for upgrades at the moment.