Delauany Triangulation - Removing points

hey,

i did a triangulation using the command: dt = delaunay(x , y);

(x and y are known vectors).

as a results i got this geometry:

now, i want to remove some of the points (actually i want to remove triangles but i undestood its impossible), let's say P1: dt(1 , :) = []; i can see in the work space that dt is changing size, but when i plot dt againg using triplot(dt , x , y) i still see P1:

why? how can i remove a bunch of points?

thanks!