Unless otherwise stipulated you will want to use the Product upgrade option
detail: Avalanche hardware upgrades a regularly put out as product upgrades. An OS upgrade will often mean an Image file and will often require a USB drive upgrade. However we have had updates that have used the OS option – theses upgrades are made very clear – from the release notes. If you have any further question regarding this procedure you will need to contact support Under Administration -> Appliances – You will see the option for Software Upgrade – once inside the Upgrade window, you will need to add the appliance IP address. Once the address is supplied – you will need to choose the PRODUCT UPGRADE file – the location if this file will vary depending on the hardware type and version you are upgrading to(so be cautious)Navigate to the TGZ directory of the version you are installing -> something like this: C:\Program Files\Spirent Communications\Spirent TestCenter 3.51\Layer 4-7 Application\TGZ\3100 (notice the Version is 3.51 and the hardware type is 3100)