[ubuntu] How do I change default drives?

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http://ubuntuforums.org – I have my 305 GB Filesystem mounted but while installing MinecraftServer.exe, my laptop said I didn't have enough room on my disk. I then went to disk usage analyser and looked at how much space I had. I had about 299 Gigs remaining. I already have the drive mounted and I have gParted but I can't partition my /dev/sda7 to a bigger size. I also don't even know if my hard drive is really being used at all. I have tons of space left but it just wont work!I'm not really sure what to do at this point because 10 GB is not enough for me to really do what I want at all! Thanks -Braeden (Hardware)