It's not free to upgrade a Superhub 2ac to a Superhub 3. It will cost £14.99. Ring up and speak to Customer Services if you'd like to order one but personally I'd stick with your 2ac as the Hub 3 has an ongoing problem with latency. There's a 248 page thread about it here.
If you do any on line gaming, DON'T "UPGRADE" TO A SUPERHUB 3. It is a ghastly pile of junk with severe problems with latency, dropped packets, and you'll have a worse gaming experience than a Superhub 2. And if you do any VOIP, video calls/conferencing or heavy streaming, they're affected, so you're best avoiding the SH3. The SH3 is afflicted by currently unresolved faults related to the Intel Puma 6 chipset, there's been no communication from Virginmedia about what if anything they can or will do, and they ignore or deny the problems.
Mind you, if you're determined, I'll swap you my Supergarbage 3 for your SH2ac.
In that case, the Hub 3 looks to be your only option. I would ring up and use the broadband faults option, explain the situation and hopefully they'll post a Hub 3 out FOC. It shouldn't cause packet loss but you will see large latency spikes every minute or so which would particularly affect online games. Having said that, it's WiFi capabilities are better than the SH2ac, so it's weighing up what you value most.
Cut your losses, ask for an SH3, pay the fifteen quid or whatever to "upgrade". You should be fine as most of the SH3 problems are with gaming. Latency is the time taken for a signal from your computer to reach a remote server, that's how long it takes for the information to reach the game server when a game player has moved, or taken a shot. Long or erratic latency is a disaster for online gamers, even though the SH3 issue is usually a momentary spike from say 25 milliseconds to 150 milliseconds ("long" is relative!). For uses other than gaming, VOIP and video calling, latency isn't often important. You might see some affects when streaming, but I suspect you'll generally be OK, and may not even notice any change. Even with video calling you'll just see a momentary stutter and probably put that down to the wider internet.
If you opt to have an SH3 you almost certainly won't be allowed to retain the SH2ac - it is VM policy now to replace SH2s with SH3s if a techy visits, but as soon as the technician sees yours is mangled, he ought to insist you relinquish it because of the H&S angle - it is VM's property, so they could be held liable if your house burned down. Even if you retained the SH2, getting it reactivated may not be straightforward.