slow internet

hello there,
i am working as a network administrator.
i have one problem. our internet is dead slow.we are using VSAT to access internet. the speed is 256/128 kbps.we are using Nortel switch layer 1 and layer3 with nortel VPN router n iDIRECT modem.
it takes ages to send one attachment by mail n same problem to open the web pages.

can anybody help me to solve this problem please?

The VSAT is routed from Hongkong.