Resizing heightmap / heightfield
Open your XYZ or ASCII Grid (ASC) heightmap terrain in L3DT and select Operations → Heightfield → Resize heightfield. Then choose new size. If you wish to change the cell size, select Operations → Heightfield → Change horizontal scale.
Calculating 4096 heightfield with 10m cell size attributes / texture layer will be very very slow. More than 1 hour of processing (this hour estimate might be over decade old hardware based heh).