You can use partition manager software to either resize that partition you have, or add one or more extra partitions using the unallocated space.
I think EaseUS has a free version, but I use an old full version of Acronis
has never let me down and I never had to grab anything newer. There are other options but if you want something completely free I would try that first one I mentioned, it seems fairly popular.
I could be wrong but I don't think that's comprehensive, which might be part of the reason it's hidden away. I think I remember reading that it couldn't move partitions...dunno if there was anything else.