"Can I remove "C""
I'm not sure if the system would still work if you did this.
But that isn't the complete issue. What would result is you'd have an unallocated area on the drive - I'm sure that's not what you want.
Do you want to end up with one large partition, and the OS on it - or what?
Can you also give us a clue as to the total drive and partition sizes please.