You get the option to boot to two different operating systems because your boot.ini was modified during the install of the second OS. You can change the boot.ini back to normal by editing it with notepad.
You can find boot.ini on drive C. If you do not see it open explorer and click on "Tools" and "Folder options". On the "View" tab, check "Show hidden files and folders" and uncheck "Hide protected operating system files".
If you attempt to delete files on E and get the message that the files are ,locked, it may mean that you are booting to E!
You need to modify boot.ini to point only to the first partition (C). Then, reboot and then, you should be able to delete files on E.