I have looked back over previous threads but can not find anyone else having this problem which means I am in serious trouble.
Normally what I have been doing (because I don't know where to find the tool) to change a size of a part after I have extruded it and moved on is undo everything, change the size and then start again. Pretty bad I know. Now it is the next day and I need to lengthen the part in one section and shorten it in another. The best way is to get to the original lengths and just change it there but I can't seem to get to that point. Also how can I change my extrude length to shorten it?

If you're going to need to edit a part after creation (even if you don't intend to, this gives the option), take advantage of associativity and rail sweep a profile instead of using primitives or simple extrusions to create your part. Editing the length of the rail changes the length of the part, editing the profile alters the cross-section. Undoing unnecessary.