Welcome to TR.

The first question back is what brand of router do you have?

For a Cisco to turn off some of the more common ports:

echo (TCP and UDP) - port 7
chargen (TCP and UDP) - port 19
daytime (TCP only) - port 13
discard (TCP and UDP) - port 9
finger - port 79
bootp - port 67/68

These can be turned off by the commands:

no service tcp-small-servers
no service udp-small-servers
no service finger
no ip bootp server

Which ports are you looking to close off?