Increasing the Speed of WAN connection

I am connecting two branch offices using an analog leased line (9600) I have Paigain DSL Nx64k modems and Motorola Vanguard 320 routers at both ends. The link is up and running but the speed is very slow. How do I improve the speeds that I am having. Is there any product I can install or anything I can do to increase or run applications across the link faster? I need help. My average speed on the link was 13kbps.