To simply shut it down, just disconnect the power cables to the power supplies and then set the power switch to standby on each of the power supplies. The LED might remain lit for about 2 minutes.
If your concern is retaining the configuration when you boot it back up again, make sure that you first save and commit the current configuration view (or another view if you prefer) by entering the following commands to the passport:
start prov
save prov
commit prov
end prov
Better still, back up the config to a centralised server - either MDM, an FTP server, etc.
Oh, and in the wise words of the NTPs on such matters:
CAUTION
Service interruption
Before you power down a switch, inform appropriate
personnel that service will be interrupted.
;-)