when the C section is full will it switch over automatically to the other half for storage
Now I love you thinking on this 😀 , as that would be kinda logical, but no sorry to disappoint you need to do some fettling..
First do some house-keeping, lots of websites specify how to do this, so I’ll leave it to them to explain in detail. This will clear up unwanted temporary files & give you some breathing space.
Next major step is to either manually moving your documents & pictures to the E drive, or you could move your profile(s) over, again a quick search of google will find detail destructions.
EDIT: oh and re-partitioning the drive into one large partition is an option, but you’d need specialist software to do it for you (and I’d want a backup of everything, including images of the partions before I started down this road).