[ubuntu] Root only has 46 k or meg, What do I need to clear some space?

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http://ubuntuforums.org – Keep getting that message of root having only so much space left and it says that I should remove some programs. To get some space back on root, what should I remove? And how? I cannot find the root directory in the disk program that comes up when I click on the investigate button. I am wondering if it is the extra kernals that are there. In the Grub message it shows 5 or six of them for 10.04. Is this the possible cause? If so, how can I clear the out dated kernals and keep only the two newest? I hope that you can help me, anybody. (Hardware)