memory is now full-how to free up some space?

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http://www.ubuntux.org – Hi everybody, I'm new to linux and new to this forum. I just started running ubuntu on a sony laptop (vaio) that is about 8 years old. After a few weeks use, the laptop stopped recognizing the hard drive. Was able to deduce that the memory is 100% full as I had done no maintenance and the temporary files and cookies must have just piled up. How do I get into that and delete the right things to free up some space? How can I do that in the future? The guy who gave me this machine and loaded it with ubuntu in the first place tells me that there is not a file cleaner to automatically do that like you would see with a windows pc. Help? (Distributions)