My machine currently has Windows 7 and Ubuntu on separate partitions. I want to get rid of the windows and have Ubuntu taking up the entire hard drive. How should I go about doing this?
It might be or might not be possible depending on your partition layout.
You can install
GParted from Ubuntu Software Center and try to delete the Windows partition and make some free space. Then you might be able to Extend the size of the Ubuntu partition.
You should do this using an Ubuntu Live CD.
You have proceed with caution. You may want to read GParted Manual
Gparted will be needed for the following. And a Ubuntu live USB/CD/DVD.
Provided the windows and Ubuntu partitions are next to each other, you should be able to delete the windows partition by right clicking on it and clicking delete, then right clicking the Ubuntu partition, select the resize/move option and using up the space windows originally had.