Hello Akash666, welcome to Seven Forums!
Have you right clicked that Free Space to see if you get a "Delete" option in the drop-down, though if it's part of an Extended partition (more than one Logical) you may not be able to create it as unallocated space; post a snip for us to have a look at.
Before we make any specific recommendations will you please post a snip/screen-shot of the entire Windows 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 maximized snip of that.
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