1. Buy ip cctv. Theyvuse p2p. You can view them remotely. Or newer wired cctv system nowadays also start to use p2p.
2. If you want to keep your old cctv, then you need to have dns account, setup port forward and then install vpn server in your router. Even if your ip is private or dynamic ip. It will work but alot of hassle.

I got both of above setup and I am slowly changing to option 1. Wireless ip cctv