It's a normal case in Disk Management. Here's the deal: Windows can only "Extend Volume" if the unallocated space is physically adjacent (immediately to the right) of the partition you want to grow. That 529MB Recovery Partition is sitting in the middle so Windows just greys out the button. And DO NOT DELETE Recovery Partition. That could kill your PC。
You don't need to format everything, but you do need to step outside of Windows' native tools to fix it. You can try some third-party partition management tools to adjust your partition space. Don't forget to back up your important stuff first.
