In Photoshop, How do you delete your work history in the current file?

Open hystory tab panel (window/history) / right click on any history state / CLEAR HISTORY.

To delete a state, click the name of the state, and choose Delete from the History panel menu. States following the one you selected are also deleted.

To delete the list of states from the History panel, without changing the image, choose Clear History from the panel menu or choose Edit > Clear > Clear History. Clearing is useful for freeing up memory, especially if you get an alert that Photoshop Elements is low on memory.