Projection not central to lens, means it's impossible to focus evenly

The projector is ceiling mounted 

The projected image comes from the very bottom of the lens (relative to the ground). So much so that the aberration caused by the edge of the lens makes it impossible to focus the entire image evenly. You can either have th bottom in focus, or the top, not both. 

The image is being projected so far off centre that the projector actually has to be pointed at the ceiling so that it can then throw the image diagonally down to the wall that's 6m away.

I've looked at the manual and it appears that there's different display settings for "PC mode" and "video mode" but nowhere in the manual does it tell you how to swap to "PC mode" ... Pressing the video mode button and switching between Presentation and Bright and custom etc does not do it.

Seems crazy that there isn't an option to shift the projection vertically. I must be missing something. Please advise.