Well you can’t extend the C: drive because unallocated space is not directly next to it on the disk and Windows Disk Management only allows you to extend a partition into adjacent unallocated space. So use disk manager for the partition or try to use a software if unallocated space is not adjacent.

Hi

I use Paragon Partition Manager CE, and view the Storage device with that.

So if you take a screenshot, and post it here, then maybe help could be given.

I use miniTool partition wizard Free tool for extend C Drive in disk management. It’s free for basic operations like this.