History+Panel

History Panel
Create a duplicate layer before you change anything but right clicking on background in the layers panel and click duplicate. When you have changed multiple things you can see what you have done. Window- History This shows the last 20 steps - you can remember up to 1000 changes but it takes more memory. Find the part you want to change, right click and delete. If you click the last similar command, you can delete all of that command. To remember more than 20 changes, click Edit - Preferences - Performance - change the numeral in History States