Hi Joe thanks for posting in the Lucidchart community! Our sincere apologies for the delayed response on this thread - I wanted to follow up in case this answer may still be useful to you and to provide a solution for other users who see this thread in the future.

If you right-click on the shape you'll see an option to 'Change Shape'. This will allow you to replace the shape with another shape in the same library. If you want to replace the shape with one from another shape library you'll need to delete the original shape and then drag out the new shape.

Let me know if you have any questions!