Any idea how to remove the 400' lock on altitude?

Do you still have it in beginner mode?

Are you trying to fly next to a restricted airspace? or some where close?

No, I am at least 10 miles away from nearest airport and its a small municipal airport.  I am out of beginner mode as well.

Change your altitude limit in the DJI App

Be careful before flying above 400feet.  

What is the max height allowed by your country aviation authority.  Could this be 400 feet !!!  If you fly above the aviation restrictions you may be placing yourself at risk of fines  

If you're good to fly in this altitude go to:
Mode -- Set maximum flight altitude.

At least in the iOS App it's necessary to be connected to the Inspire 1 otherwise your setting wouldn't be updated.