Ken Moiarty wrote:
My shower lacks pressure so I want to replace the existing 1/2 inch copper
pipe that leads up to it with 3/4 inch copper pipe. Obviously, if done
correctly this will increase the water pressure available at my shower.

Increasing diameter increases flow, not pressure. Pressure is
determined by head, or height of fixture relative to height of water
source if no pumps are used. Increase pressure by having your
town buy a new water tower.

Increasing to 3/4" would be useful for multiple showerhead fixtures.