Removing a State and Clearing All States in Photoshop

To remove a state and all the steps that follow it, select the state and then do one of the following:
-->Press the Delete key.
-->Click the trash can icon.
-->Drag the state’s icon to the trash can icon.
-->Right-click the state (or Control+click on the Mac) and choose Delete from the contextsensitive menu that pops up.
-->Choose Delete from the History palette pop-up menu.

Clearing all states
You can clear all the states from the palette by choosing Clear History from the palette pop-up menu. To delete all the states except the last one in the history list, as well as keep the snapshots you’ve saved, choose Edit➪Purge➪Histories. You can clear or purge your history list when you don’t need the states that are included anymore, to save memory or to return to the original state of your document. Just be sure you’re really, seriously, not interested in going back again later to make changes because this command cannot be undone, with one exception. You can only undo your clearing or purging if you choose Edit➪Undo immediately after you execute the command.