Hello TKoomen, welcome to Seven Forums!
Before we make any specific recommendations will you please post a snip/screen-shot of the entire disk management drive map with a full description as to which drive/partition is which, so we can see what you have going on as there may be a fairly simple way to resolve the situation.
In the Windows start menu right click computer and click manage, in the left pane of the "Computer Management" window that opens click disk management and post a snip of that. How to Upload and Post a Screenshot and File in Seven Forums
Be sure to post back with any further questions you may have and to keep us informed.