You are welcome to download the latest software from the Telium website, and overwrite your installation. Please be sure to carefully compare the included config file to check for changes in stanzas, key names, new keys, etc.
If you are running the Free Edition the new software will work immediately. If you have an active maintenance agreement then the upgrade will work as well.
However, if your maintenance agreement has expired then the upgrade will revert to the Free Edition. Since you cannot extend a maintenance agreement that has expired you would have to purchase a new license.
If your maintenance agreement is still active then you can extend it for as long as you like (purchased in 1 year increments from the BUY tab on the Telium web site).