If that is the only partition you have, you can't increase it without buying a new drive. Uninstall programs you don't use any more. Also you can reduce the size of space the Recycle Bin and System Restore reserves. Also change the size of the temporary internet file area, 100mb should be fine, it's usually set to 1 gig or something.
My c partition is filled in red and saying it's full but I cant increase the size of my acer drive (c partition?
What's your OS? If your OS is windows 7 the snap-in disk management could hlep you increase partition size when there's an unallocated space at the end of the partition which you want to extend, or you could refer to this article about how to solve C drive full