Dedicate more hard drive space to Ubuntu

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http://www.ubuntux.org – I was running Windows 7 on my laptop but installed Ubuntu Linux as well. While installing Ubuntu I made an error and only dedicated 17 Gigs of hard drive space to Ubuntu and the rest to Windows. I would like to split my hard drive more evenly but cannot seem to figure out how to reconfigure Ubuntu to use more than the 17 Gigs. Any guidance would be greatly appreciated. Thanks! (Distributions)