How to Extend a Partition to Fill a Computer Drive
Right-click your C: partition and choose Extend Volume from the pop-up menu that appears.
The Extend Volume Wizard appears, ready to walk you through the process of extending your C partition to fill the entire drive. Click Next to start the wizard. The wizened wizard is sharp enough to know you want to extend your drive into the vacant space, so it offers you that option with its first screen.