Hi Harry,
All previous Firmware is stored locally on your computer. Do a search for TC-Helicon (search hidden files/folders too). You should find a folder with that name that contains a VoiceSupport folder, with your product listed within it. Inside that is the Update Files folder, which will have copies of your firmware versions that you can point to via VoiceSupport if you choose "Load Firmware Manually" from the Firmware options.
For me it's C:\Users\XXXYourNameXXX\AppData\Roaming\TC-Helicon\VoiceSupport\VoiceLive 2\Update Files
Here's the thing, as we've progressed through firmware, we've added parameters, changed memory allocations etc. etc. so there's no guarantee that your presets will port back and forth between versions. Make sure you back all your presets up before upgrading, so you can re-import them if you decide to downgrade.
-Craig