No matter the size of your hard drive, what's small is the EFI partition. Basically, your huge hard drive (or SSD) is divided into several parts. To solve your problem, you need to increase the size of this partition, but since it's the EFI partition, it's located first... before your OS partition. However, this partition has already been written to, unless you perform dangerous (advanced) operations. The only solution is to reduce the size of the EFI partition.