Cisco 2911 VPN help

Hi folks! I'm in some fairly urgent need of assistance with an issue I'm having and I figured I'd post here and hopefully some of you can help a brother out. :)

So, I recently inherited a pretty scattered IT department for an SMB and the ISP had informed them months ago that they were closing down the subnet that their WAN IP was on. The ISP informed them of their new IPs and told them they needed to change them to avoid service interruption. Well, lo and behold, no one ever did anything with that info so last night, the ISP shut down that subnet and this morning, no internet. I spent a little time digging through the network trying to diagnose the issue and discovered what the problem was upon calling the ISP. I changed the IP out in the Barracuda firewall at the main office and everything was back online.

Now for the problem. We have an office in Canada that has a Cisco 2911 and there was an IPSec VPN tunnel between the Barracuda at the main office and the Cisco at the Canada office. Now that the WAN IP has changed on the main office, the VPN is obviously kaput. I know I need to go in and modify the VPN on the Cisco side to reflect the change in the IP, but I know absolutely zero about configuring Cisco gear without a GUI. I'm sure I'll take quite the flogging for being that guy that hasn't taken the time to learn Cisco yet. It's on my to do list, but in the meantime, I need to get this VPN back up asap. I imagine there are only a couple of simple commands to get this done, but I have no idea what they are. I've tried to read through the Cisco documentation for the 2911, but it really only gives details on setting up a VPN and it's all pretty confusing to me. I thought maybe someone might have a more simplistic way of explaining it that would help me get this done with a minimum of hair pulling and jumping about.

Thanks in advance for any and all help!!