We never recommend doing ANY changes to a live system. All changes, even policy changes, should be done under proper change control management procedures to evaluate and avoid risk.

Having said that, all product releases include a change log which will explain the risk level and minor upgrades can generally be done to a live system if you are prepared to take the risk. Generally speaking minor upgrades are unlikely to cause problems which can affect service and are rated low risk. Major updates are high risk and should never be done while online or in service. A reboot may be required or even a visit to the nearest Opteq partner.