Installed ubuntu on drive C, but
 

drive E: still is running windows. How can I completely delete windows from my computer? Sorry for the noob question.

Welcome to LQ!!

First, stop thinking about drives and partitions in the Windows way. Using "fdisk -l" in a terminal, you find that Linux is on /dev/sdaX and Windows is on /dev/sdaY. (X and Y being partition numbers)

To delete Windows, all you have to do is delete that partition.

For more specific help, post the output of "sudo fdisk -l" (Run this command in a terminal, which you will find somewhere in your menus)

First, stop thinking about drives in terms of drive letters, they do not exist in Linux.

In the Linux distro's installer there should have been a choice to use up the whole drive. You xhould be able to delete the Windows partition, I don't know how you would enlarge the Linux partition(s).

i think gparted can help you.