Is it safe to change wind blowing direction of a William Wall Mounted Heater?
Normal heaters of this type use natural convection: input at the bottom, output at the top.  The vanes are bent for that purpose.    However, this has a problem; it doesn't provide any room circulation, and hot air tends to "hang out" at the ceiling, where it can be 10 degrees warmer than air at the floor.  

It doesn't take much to stir the air in the room; I use a "muffin fan" from a PC power supply.  

What you have there is Williams' attempt to correct that.  It's called Forsaire, and it indeed has an electric forced-air blower.  This creates a reverse flow.  Now, cold air is taken at the ceiling, heated and dumped at the floor.  And you don't like that. 

Depending on your model, the furnace may function during power loss.  Those models keep the thermocouple and millivolt thermostat from the convection models, and will cheerfully fire and burn the burner with no power at all.  Normally, the blower detects the heat and runs the blower at that point; however if the power is out, that doesn't happen, and it makes do with convection. Kinda cool actually; I've seen it. And if I recall, the manual specifically says you can do that.  In this operating mode, airflow is convection: out the bottom, up the top. That's what you want, yes? 

Some models of this furnace make the 24V thermostat power mandatory; obviously they won't fire during AC power loss. 

So you might want to consult your furnace's manual, or contact the factory, and see if yours can operate this way. 

Also, ask the factory about alternate doors which will give you flow in a different direction.  They actually sell those: check out diffuser grille kits 6703 or 6704, or side grille kit 6702. 

If cost were no object, I'd say swap this for a passive Williams unit, since you don't even like the Forsaire feature.  But that's a $700-900 deal depending on the size of the unit and if it's double-sided.