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I am not sure what you mean about the side bar, but to modify the top bar, open themes/yourtheme/theme.html and edit the top bar part.
If you mean (Regarding the side bar) that you want to put something in it, go to the admin panel > system > blocks > add new block (At the bottom of the page). To put the block in the sidebar, just set the block side to left.
Not sure if this is what you wanted, but hope it helps,
Aubrey