Upload shaping for each lan users

[bsd3000]

Hi all
I have ADSL LINK  7Mbit download 0.7Mbit upload.
PfSense does nat for LAN users to user ADSL link
Sometimes it happens that a user performs an upload from lan and take all the upload bandwidth,
this giving problems to all others users who want surf internet
How can I do to make a user's LAN can not upload files taking up all the bandwidth?
(LAN users are about 20 and have dynamic dhcp ip from pfsense)

thanks