There are other freeware partition managers out there. gparted is one of the more popular and probably the best as well. However, some users don't find it as user-friendly for newbies.
One such tool is Minitool Partition Wizard Home Edition. Another is EASEUS Partition Master (Home Edition). This might give you other ideas on what to try as partitioning tool:
Split External HDD that already partitioned | Techyv.com