Well I've got a 750 GB Hihachi HDD. I've installed Ubuntu on one of it's partitions (space dedicated to it is 50 GB). Now all of the other space which will be about 643 GB has become System Reserved which I want to split it into some other partitions and install Windows 8.1 on it. I guess if I try to delete this partition, some critical manufacturer system data will vanish. How should I fix this problem? Should I boot a partition manager disk and shrink this System partition? Wouldn't system data be deleted in that case?
PS: This is my current partitioning state: