I have an ADSL access point modem(D-link DSL 2640T) at my home that Valid IP address is assigned on it.

Also two PCs connect through the ADSL Modem access point to Internet.

I want make remote desktop connection to one of the PCs from Intenet outside my home.

Meanwhile the two PCs get private IP from ADSL access point Modem DHCP.

Could you please help me how can I do it?

You need to forward the appropriate ports to the computer you want to access from the internet. Check this site for more details:
PortForward.com - Free Help Setting up Your Router or Firewall