The easier way to resize it is boot in single mode and then do it from the command line. What filesystem type is it? ext3? reiserfs? etc, etc?
I just deleted home and resized /var to use the space /home was using on an install I had. For you however, it's easy, since you just need to change /home mountpoint to /usr instead. Do this:
1. Tar the contents of /home like this:
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tar cvjpf home.tar.bz2
those parametes will make a bzip2 file and will keep the permissions on all files for when you extract them again. It's important for any user accounts you have on your system.
2. Make a directory called /usr2 and unmount /home and mount it to /usr2 removing the contents of /home since you don't need anymore. Copy the contents of /usr to /usr2 like this:
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cp -dpRx /usr/* /usr2/
again, this will keep permissions on all files. Now, edit /etc/fstab and create entry for /usr. Unmount /usr2. Remove the existing contents /usr and reboot your system. Untar the home.tar.bz2 to /home. All this will have to be done from rescue cd or similar.
Alternatively, if you need to keep /home, then I suggest you use the command line resize tools, but it's not as easy as you think since you then have to use fdisk to delete, and then recreate the partition smaller than it was, but big enough to accommodate what data is already there. Also, perhaps parted will do what you need, but again rescue or single user mode to do this.
And remember, backup your data in case it goes wrong.