remove white from a architectural plan sheet

[Amuzed_Bob]

I have a png of an architectural floor plan. So, it's black lines on a white page. There are hundred of spaces that are white surround by lines that provide the 2D view of what ever object it is. Such as white between the lines on either side of a wall, or a cabinet, or some furniture. If I select by color by clicking a particular white space, that specific white space out of hundreds is selected. If I click and drag, the whole page is selected and I end up deleting the lines too, which is what I want to preserve. And all I want to preserve.

There must be a way to do this. Newbie apologies if it's drop dead easy...