In Visio, you can replace any existing shape with an entirely different shape and yet retain all of the original shape's key characteristics—position, connections, formatting, shape text, and shape data.
In your diagram, select the shape or shapes you want to replace.
On the Home tab, in the Editing group (on the far right end), select Change Shape:
A drop-down menu shows you a gallery of related shapes to choose from. You can switch categories to see a different group of shapes.
Select the shape you want to switch to.
You can only replace 2D shapes with other 2D shapes (like a Decision shape for a Process shape) and 1D shapes with other 1D shapes (replacing one type of connector with another). You cannot replace a connector with a rectangle, as an example.
This feature is available in Visio 2013 and newer versions. It isn't available in Visio 2010.