Paula is quite right - you can configure the history to record all changes you have made to you image but changes made in previous sessions can only be recorded textually in a log file>
So as far as I'm aware you can't record the actual changes made in a previous session so that they can be clicked and reverted to in the new session.
The text information recorded in the log file follows this format so you can see what editing stages you have performed on what day and at what time - if that is any use to you

.....................
2010-07-24T11:33:59+01:00 File C:\Users\Roger\Documents\Pictures\golf.psd saved
2010-07-24T11:34:05+01:00 File golf.psd opened
Open C:\Users\Roger\Documents\Pictures\golf.psd
Select Canvas
Set Selection To: all
Stroke
Stroke Width: 6
Location: inside
Opacity: 100%
Mode: normal
Color: HSB color
Hue: 0°
Saturation: 0
Brightness: 99.608
2010-07-24T11:34:41+01:00 File C:\Users\Roger\Documents\Pictures\golf.psd saved
2010-07-24T11:40:15+01:00 File golf.psd opened
Open C:\Users\Roger\Documents\Pictures\golf.psd