I'd simply save copies of the running configuration - "show running-config" and copy and paste the data out of your terminal window. Also be sure to save it as the startup configuration - "copy running-config startup-config" so it survives if the router needs to be rebooted.
I have been in Cisco networking for a long time...there are two solutions I can think of that work relatively well for this. One is a commercial solution that works really well and costs a small amount of money. The other is a free linux based solution which doesn't cost any money, but it takes a pretty good amount of linux knowledge to set it up and get it working. The commercial solution is Kiw iCAT Tools which is owned by SolarWinds now. This solution runs on Windows and is relatively easy to setup. It will backup your configurations automatically on a schedule and then email you if there is a change. Personally for the money I think it costs about 600 dollars I would use Kiwi Cat Tools. The other solution is called RanCID. Rancid is a program that runs in the crontab of a linux box and does basically the same thing. Rancid works well but it can be a real pain to setup if you don't know linux very well and it is not for the faint of heart. Personally I have used both and would prefer Kiwi. I currently use RanCID because I didn't want to spend the money for Kiwi and I am pretty good with Linux.
I'd start with "write erase" or "erase start", and follow that up with "reload".