Well for one, it would help to know what operating system you are using. WIndows 7? Windows XP? a mac??
Let's assume you have Windows Vista, XP or 7.
Now for one, just to be sure you're seeing everything, in case something is hidden, start with this.
start menu (globe bottom left corner of your screen) & click on the "documents" folder.
steps
Start Menu>Documents>Tools>
choose the "View" tab
uncheck anything that says "hide"
check anything that says "display."
also be sure under "hidden files and folders" the option is selected "show hidden files, folders or drives."
This will change your settings so nothing is hidden, that you want to look for.
Here is a useful "how to" video, on how to remove the partition.
http://www.youtube.com/watch?v=vIWh5sFdtcw
Now if you have a specific operating system, you might do your own search in youtube just type in the search menu, "how to remove partition from Windows __________" (your operating system)
This should fix your issue.
Another couple of things you can do to get your computer running better/faster:
DISK CLEAN UP
start menu>control panel
type in "clean up"
choose "free up disk space by deleting unnecessary files"
then of course, select your C drive, wait for it to search.
Then, choose what you want to clean out from the cluttered areas & let it do its thing.
If you're going to select the computer to delete a lot of stuff, you want to first, be sure to save some place (a document is good), all of your passwords & login information, so if the automatic sign in's are set up, that you keep a master in one area, of every single thing you log in to IE; banking, ebay, paypal, email, facebook, etc. This is a terrific habit to have. You can also, if you use MS Word to keep a master password document, to password protect it. This will only work if you have the full version of Word, not the "starter" version. You can find how to password protect your document either in the help menu or simply do a lookup in youtube on how to do this with what your version is. You locate it in word when you click on "save as" then go to the tools area. I would just put a password for opening the document, but not for anything else (like editing the document)
You also might wish to defragment your hard drive, to take all the things you've done over a long period of time, to get all of your files sorted & free up a lot of wasted space, this will cause your computer to run faster once it's finished.
DEFRAGMENT
Start>All files>Accessories>System tools>disk defragmenter
Just let this run until it finishes at a time you will be able to walk away from your computer for awhile, to let it run for a long time until it's finished. Then select what you want cleaned up, but again, be sure all of your passwords are saved in one central area first.
Also, be sure you have anti-virus software,, a great one that is free is AVG you can get the "basic" version (not a trial) & also be sure your firewall is turned on. Start>control panel> type in the search window "firewall" then click on firewall. If everything is green & says it's on, you're fine. if it is not on, select that it be on.
Hope this helps!