Right-click the taskbar and make sure the Lock Taskbar option is unchecked, then click-and-drag the edge of the taskbar to resize it. Then just right-click the taskbar and check the Lock Taskbar option to prevent future mishaps.
Hope this helps,
My mother wanted to use my computer and she can't operate a computer correctly to save her life. She must have been looking for something and now she has stretched my start menu all the way to the top of the screen somehow and it looks very ugly.