If the display is 1440p, 2560×1440 is its native resolution.
You can't "make the pixels smaller". They are what they are.
Seems to me that if you "forced it" into HiDPI mode -- in which 2 pixels are used in place of one, both horizontally and vertically, you would end up with a working resolution of only 1280 x 720.
Is this what you want?
If you want greater resolution than 1440p, you have to go to a display that is 3840×2160 (UHD, Ultra HD, 4K, 2160p).