You can manually delete snapshots that you no longer need or to make more disk space available.
The virtual disk files that a snapshot creates do not contain the entire contents of the virtual machine's virtual disk. When you delete a snapshot, you must consolidate the changes that it captured into the original, parent virtual disk.
You cannot delete the snapshot showing the "Current State" of the virtual machine.
Allocate enough time for virtual disk consolidation. If a snapshot captured a state considerably different from the earlier state, for example, a service pack upgrade, the consolidation might take up to a few hours.