How to setup?

Attn: to whom may concern

Our company having a problem in "opening port" for the router. Actually, we
doing the CCTV security product (surveillance system).
Our situation like this: our office fix up a camera together with the
surveillance system, but, we fail to dial back from anywhere (home or other
places) to look back from office.

Our company using item like below:
D-Link DI-704P (Router)
D-Link DSL-500G (Router with ADSL Modem)
24 Port hub 10Mps
7 units PC
ADSL Line (Dynamic IP)

Thanks...!!

ITS Technology (M) S/B
EricTung