Do you want to login for maintance or to do some thing else?
Normally, in order to log in to a network work device, the first thing that needs to be done is, have your ISP change your IP to a static.
Then In the ISP modem, you need to set it to bridge mode, now it the modem is a combo router wireless, when going to bridge it will disable the router/wireless.
That means that your main router will now be the Cisco.
When you have done all the above, log into the ISP modem and go to advanced >port forward and set up the following ports to what ever your Cisco IP is.
IE: from ISP to Cisco 192.168.0.153 so from/to IP is 192.168.0.153 port 80 both tcp & UDP, then do the same for 443, 1723, 1891 and you may need one or two more.
Once this is all done, do a power reset of both the IPS madem and the Cisco.
Now on your computer, go to network connections and set up a new connect for VPN using the IP assigned to your system from your ISP>64.662.65.23
Using that IP, you should be able to go any where connect to an access point and connect to your cisco, then once connected you can do what you want.