Believe it or not, you have to remove the failsafe rod, then loosen the clamp on the measure, then remove the measure and pour the remaining powder into the powder keg, probably using a funnel.
I know, mickey mouse, but that's the way it is.
Then go to Unique Tek and buy the Powder Measure Drain-N-Change Tool so you never have to do the mickey mouse stuff again.
http://uniquetek.com/product/T1347
$17.95
While you're at unique tek, buy a micrometer bar for the powder measure too so you can get away from the other mickey mouse part of the powder system, the 7/16" wrench to adjust the drop.